[Qemu-devel] [RFC 2/2] KVM, MCE, unpoison memory address across reboot

[Huang Ying]

In Linux kernel HWPoison processing implementation, the virtual
address in processes mapping the error physical memory page is marked
as HWPoison.  So that, the further accessing to the virtual
address will kill corresponding processes with SIGBUS.

If the error physical memory page is used by a KVM guest, the SIGBUS
will be sent to QEMU, and QEMU will simulate a MCE to report that
memory error to the guest OS.  If the guest OS can not recover from
the error (for example, the page is accessed by kernel code), guest OS
will reboot the system.  But because the underlying host virtual
address backing the guest physical memory is still poisoned, if the
guest system accesses the corresponding guest physical memory even
after rebooting, the SIGBUS will still be sent to QEMU and MCE will be
simulated.  That is, guest system can not recover via rebooting.

In fact, across rebooting, the contents of guest physical memory page
need not to be kept.  We can allocate a new host physical page to
back the corresponding guest physical address.

This patch fixes this issue in QEMU-KVM via calling qemu_ram_remap()
to clear the corresponding page table entry, so that make it possible
to allocate a new page to recover the issue.

Signed-off-by: Huang Ying <address@hidden>
---
 kvm.h             |    2 ++
 qemu-kvm.c        |   37 +++++++++++++++++++++++++++++++++++++
 target-i386/kvm.c |    2 ++
 3 files changed, 41 insertions(+)

--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -1803,6 +1803,7 @@ int kvm_on_sigbus_vcpu(CPUState *env, in
                 hardware_memory_error();
             }
         }
+        kvm_hwpoison_page_add(ram_addr);
         mce.addr = paddr;
         r = kvm_set_mce(env, &mce);
         if (r < 0) {
@@ -1841,6 +1842,7 @@ int kvm_on_sigbus(int code, void *addr)
                     "QEMU itself instead of guest system!: %p\n", addr);
             return 0;
         }
+        kvm_hwpoison_page_add(ram_addr);
         status = MCI_STATUS_VAL | MCI_STATUS_UC | MCI_STATUS_EN
             | MCI_STATUS_MISCV | MCI_STATUS_ADDRV | MCI_STATUS_S
             | 0xc0;
--- a/qemu-kvm.c
+++ b/qemu-kvm.c
@@ -1619,6 +1619,42 @@ int kvm_arch_init_irq_routing(void)
 }
 #endif
 
+struct HWPoisonPage;
+typedef struct HWPoisonPage HWPoisonPage;
+struct HWPoisonPage
+{
+    ram_addr_t ram_addr;
+    QLIST_ENTRY(HWPoisonPage) list;
+};
+
+static QLIST_HEAD(hwpoison_page_list, HWPoisonPage) hwpoison_page_list =
+    QLIST_HEAD_INITIALIZER(hwpoison_page_list);
+
+static void kvm_unpoison_all(void *param)
+{
+    HWPoisonPage *page, *next_page;
+
+    QLIST_FOREACH_SAFE(page, &hwpoison_page_list, list, next_page) {
+        QLIST_REMOVE(page, list);
+        qemu_ram_remap(page->ram_addr, TARGET_PAGE_SIZE);
+        qemu_free(page);
+    }
+}
+
+void kvm_hwpoison_page_add(ram_addr_t ram_addr)
+{
+    HWPoisonPage *page;
+
+    QLIST_FOREACH(page, &hwpoison_page_list, list) {
+        if (page->ram_addr == ram_addr)
+            return;
+    }
+
+    page = qemu_malloc(sizeof(HWPoisonPage));
+    page->ram_addr = ram_addr;
+    QLIST_INSERT_HEAD(&hwpoison_page_list, page, list);
+}
+
 extern int no_hpet;
 
 static int kvm_create_context(void)
@@ -1703,6 +1739,7 @@ static int kvm_create_context(void)
         }
 #endif
     }
+    qemu_register_reset(kvm_unpoison_all, NULL);
 
     return 0;
 }
--- a/kvm.h
+++ b/kvm.h
@@ -221,4 +221,6 @@ int kvm_irqchip_in_kernel(void);
 
 int kvm_set_irq(int irq, int level, int *status);
 
+void kvm_hwpoison_page_add(ram_addr_t ram_addr);
+
 #endif