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@@ -32,11 +32,14 @@ struct kmmio_fault_page {
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struct list_head list;
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struct list_head list;
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struct kmmio_fault_page *release_next;
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struct kmmio_fault_page *release_next;
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unsigned long page; /* location of the fault page */
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unsigned long page; /* location of the fault page */
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+ bool old_presence; /* page presence prior to arming */
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+ bool armed;
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/*
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/*
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* Number of times this page has been registered as a part
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* Number of times this page has been registered as a part
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* of a probe. If zero, page is disarmed and this may be freed.
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* of a probe. If zero, page is disarmed and this may be freed.
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- * Used only by writers (RCU).
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+ * Used only by writers (RCU) and post_kmmio_handler().
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+ * Protected by kmmio_lock, when linked into kmmio_page_table.
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*/
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*/
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int count;
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int count;
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};
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};
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@@ -105,57 +108,85 @@ static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
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return NULL;
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return NULL;
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}
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}
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-static void set_page_present(unsigned long addr, bool present,
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- unsigned int *pglevel)
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+static void set_pmd_presence(pmd_t *pmd, bool present, bool *old)
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+{
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+ pmdval_t v = pmd_val(*pmd);
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+ *old = !!(v & _PAGE_PRESENT);
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+ v &= ~_PAGE_PRESENT;
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+ if (present)
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+ v |= _PAGE_PRESENT;
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+ set_pmd(pmd, __pmd(v));
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+}
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+
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+static void set_pte_presence(pte_t *pte, bool present, bool *old)
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+{
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+ pteval_t v = pte_val(*pte);
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+ *old = !!(v & _PAGE_PRESENT);
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+ v &= ~_PAGE_PRESENT;
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+ if (present)
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+ v |= _PAGE_PRESENT;
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+ set_pte_atomic(pte, __pte(v));
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+}
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+
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+static int set_page_presence(unsigned long addr, bool present, bool *old)
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{
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{
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- pteval_t pteval;
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- pmdval_t pmdval;
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unsigned int level;
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unsigned int level;
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- pmd_t *pmd;
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pte_t *pte = lookup_address(addr, &level);
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pte_t *pte = lookup_address(addr, &level);
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if (!pte) {
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if (!pte) {
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pr_err("kmmio: no pte for page 0x%08lx\n", addr);
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pr_err("kmmio: no pte for page 0x%08lx\n", addr);
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- return;
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+ return -1;
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}
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}
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- if (pglevel)
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- *pglevel = level;
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-
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switch (level) {
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switch (level) {
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case PG_LEVEL_2M:
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case PG_LEVEL_2M:
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- pmd = (pmd_t *)pte;
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- pmdval = pmd_val(*pmd) & ~_PAGE_PRESENT;
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- if (present)
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- pmdval |= _PAGE_PRESENT;
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- set_pmd(pmd, __pmd(pmdval));
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+ set_pmd_presence((pmd_t *)pte, present, old);
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break;
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break;
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-
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case PG_LEVEL_4K:
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case PG_LEVEL_4K:
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- pteval = pte_val(*pte) & ~_PAGE_PRESENT;
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- if (present)
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- pteval |= _PAGE_PRESENT;
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- set_pte_atomic(pte, __pte(pteval));
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+ set_pte_presence(pte, present, old);
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break;
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break;
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-
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default:
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default:
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pr_err("kmmio: unexpected page level 0x%x.\n", level);
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pr_err("kmmio: unexpected page level 0x%x.\n", level);
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- return;
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+ return -1;
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}
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}
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__flush_tlb_one(addr);
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__flush_tlb_one(addr);
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+ return 0;
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}
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}
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-/** Mark the given page as not present. Access to it will trigger a fault. */
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-static void arm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
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+/*
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+ * Mark the given page as not present. Access to it will trigger a fault.
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+ *
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+ * Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the
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+ * protection is ignored here. RCU read lock is assumed held, so the struct
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+ * will not disappear unexpectedly. Furthermore, the caller must guarantee,
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+ * that double arming the same virtual address (page) cannot occur.
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+ *
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+ * Double disarming on the other hand is allowed, and may occur when a fault
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+ * and mmiotrace shutdown happen simultaneously.
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+ */
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+static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
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{
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{
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- set_page_present(page & PAGE_MASK, false, pglevel);
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+ int ret;
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+ WARN_ONCE(f->armed, KERN_ERR "kmmio page already armed.\n");
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+ if (f->armed) {
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+ pr_warning("kmmio double-arm: page 0x%08lx, ref %d, old %d\n",
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+ f->page, f->count, f->old_presence);
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+ }
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+ ret = set_page_presence(f->page, false, &f->old_presence);
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+ WARN_ONCE(ret < 0, KERN_ERR "kmmio arming 0x%08lx failed.\n", f->page);
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+ f->armed = true;
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+ return ret;
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}
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}
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-/** Mark the given page as present. */
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-static void disarm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
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+/** Restore the given page to saved presence state. */
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+static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
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{
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{
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- set_page_present(page & PAGE_MASK, true, pglevel);
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+ bool tmp;
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+ int ret = set_page_presence(f->page, f->old_presence, &tmp);
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+ WARN_ONCE(ret < 0,
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+ KERN_ERR "kmmio disarming 0x%08lx failed.\n", f->page);
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+ f->armed = false;
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}
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}
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/*
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/*
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@@ -202,28 +233,32 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
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ctx = &get_cpu_var(kmmio_ctx);
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ctx = &get_cpu_var(kmmio_ctx);
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if (ctx->active) {
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if (ctx->active) {
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- disarm_kmmio_fault_page(faultpage->page, NULL);
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if (addr == ctx->addr) {
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if (addr == ctx->addr) {
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/*
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/*
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- * On SMP we sometimes get recursive probe hits on the
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- * same address. Context is already saved, fall out.
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+ * A second fault on the same page means some other
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+ * condition needs handling by do_page_fault(), the
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+ * page really not being present is the most common.
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*/
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*/
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- pr_debug("kmmio: duplicate probe hit on CPU %d, for "
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- "address 0x%08lx.\n",
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- smp_processor_id(), addr);
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- ret = 1;
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- goto no_kmmio_ctx;
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- }
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- /*
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- * Prevent overwriting already in-flight context.
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- * This should not happen, let's hope disarming at least
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- * prevents a panic.
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- */
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- pr_emerg("kmmio: recursive probe hit on CPU %d, "
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+ pr_debug("kmmio: secondary hit for 0x%08lx CPU %d.\n",
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+ addr, smp_processor_id());
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+
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+ if (!faultpage->old_presence)
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+ pr_info("kmmio: unexpected secondary hit for "
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+ "address 0x%08lx on CPU %d.\n", addr,
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+ smp_processor_id());
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+ } else {
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+ /*
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+ * Prevent overwriting already in-flight context.
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+ * This should not happen, let's hope disarming at
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+ * least prevents a panic.
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+ */
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+ pr_emerg("kmmio: recursive probe hit on CPU %d, "
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"for address 0x%08lx. Ignoring.\n",
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"for address 0x%08lx. Ignoring.\n",
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smp_processor_id(), addr);
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smp_processor_id(), addr);
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- pr_emerg("kmmio: previous hit was at 0x%08lx.\n",
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- ctx->addr);
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+ pr_emerg("kmmio: previous hit was at 0x%08lx.\n",
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+ ctx->addr);
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+ disarm_kmmio_fault_page(faultpage);
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+ }
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goto no_kmmio_ctx;
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goto no_kmmio_ctx;
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}
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}
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ctx->active++;
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ctx->active++;
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@@ -244,7 +279,7 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
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regs->flags &= ~X86_EFLAGS_IF;
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regs->flags &= ~X86_EFLAGS_IF;
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/* Now we set present bit in PTE and single step. */
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/* Now we set present bit in PTE and single step. */
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- disarm_kmmio_fault_page(ctx->fpage->page, NULL);
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+ disarm_kmmio_fault_page(ctx->fpage);
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/*
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/*
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* If another cpu accesses the same page while we are stepping,
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* If another cpu accesses the same page while we are stepping,
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@@ -275,7 +310,7 @@ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
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struct kmmio_context *ctx = &get_cpu_var(kmmio_ctx);
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struct kmmio_context *ctx = &get_cpu_var(kmmio_ctx);
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if (!ctx->active) {
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if (!ctx->active) {
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- pr_debug("kmmio: spurious debug trap on CPU %d.\n",
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+ pr_warning("kmmio: spurious debug trap on CPU %d.\n",
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smp_processor_id());
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smp_processor_id());
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goto out;
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goto out;
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}
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}
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@@ -283,7 +318,11 @@ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
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if (ctx->probe && ctx->probe->post_handler)
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if (ctx->probe && ctx->probe->post_handler)
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ctx->probe->post_handler(ctx->probe, condition, regs);
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ctx->probe->post_handler(ctx->probe, condition, regs);
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- arm_kmmio_fault_page(ctx->fpage->page, NULL);
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+ /* Prevent racing against release_kmmio_fault_page(). */
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+ spin_lock(&kmmio_lock);
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+ if (ctx->fpage->count)
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+ arm_kmmio_fault_page(ctx->fpage);
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+ spin_unlock(&kmmio_lock);
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regs->flags &= ~X86_EFLAGS_TF;
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regs->flags &= ~X86_EFLAGS_TF;
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regs->flags |= ctx->saved_flags;
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regs->flags |= ctx->saved_flags;
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@@ -315,20 +354,24 @@ static int add_kmmio_fault_page(unsigned long page)
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f = get_kmmio_fault_page(page);
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f = get_kmmio_fault_page(page);
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if (f) {
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if (f) {
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if (!f->count)
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if (!f->count)
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- arm_kmmio_fault_page(f->page, NULL);
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+ arm_kmmio_fault_page(f);
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f->count++;
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f->count++;
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return 0;
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return 0;
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}
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}
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- f = kmalloc(sizeof(*f), GFP_ATOMIC);
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+ f = kzalloc(sizeof(*f), GFP_ATOMIC);
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if (!f)
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if (!f)
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return -1;
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return -1;
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f->count = 1;
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f->count = 1;
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f->page = page;
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f->page = page;
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- list_add_rcu(&f->list, kmmio_page_list(f->page));
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- arm_kmmio_fault_page(f->page, NULL);
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+ if (arm_kmmio_fault_page(f)) {
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+ kfree(f);
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+ return -1;
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+ }
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+
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+ list_add_rcu(&f->list, kmmio_page_list(f->page));
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return 0;
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return 0;
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}
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}
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@@ -347,7 +390,7 @@ static void release_kmmio_fault_page(unsigned long page,
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f->count--;
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f->count--;
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BUG_ON(f->count < 0);
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BUG_ON(f->count < 0);
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if (!f->count) {
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if (!f->count) {
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- disarm_kmmio_fault_page(f->page, NULL);
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+ disarm_kmmio_fault_page(f);
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f->release_next = *release_list;
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f->release_next = *release_list;
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*release_list = f;
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*release_list = f;
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}
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}
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