[Qemu-devel] [PATCH uq/master 2/2] MCE, unpoison memory address across reboot

[Huang Ying <ying.huang@intel.com>]

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 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 <ying.huang@intel.com>
---
 kvm.h             |    2 ++
 target-i386/kvm.c |   39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -580,6 +580,42 @@ static int kvm_get_supported_msrs(void)
     return ret;
 }
 
+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);
+
+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);
+    }
+}
+
+static 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);
+}
+
 int kvm_arch_init(void)
 {
     uint64_t identity_base = 0xfffbc000;
@@ -632,6 +668,7 @@ int kvm_arch_init(void)
         fprintf(stderr, "e820_add_entry() table is full\n");
         return ret;
     }
+    qemu_register_reset(kvm_unpoison_all, NULL);
 
     return 0;
 }
@@ -1940,6 +1977,7 @@ int kvm_on_sigbus_vcpu(CPUState *env, in
                 hardware_memory_error();
             }
         }
+        kvm_hwpoison_page_add(ram_addr);
 
         if (code == BUS_MCEERR_AR) {
             /* Fake an Intel architectural Data Load SRAR UCR */
@@ -1984,6 +2022,7 @@ 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);
         kvm_mce_inj_srao_memscrub2(first_cpu, paddr);
     } else
 #endif
--- a/kvm.h
+++ b/kvm.h
@@ -188,6 +188,8 @@ int kvm_physical_memory_addr_from_ram(ra
                                       target_phys_addr_t *phys_addr);
 #endif
 
+void kvm_unpoison_all(void *param);
+
 #endif
 int kvm_set_ioeventfd_mmio_long(int fd, uint32_t adr, uint32_t val, bool assign);