[Qemu-devel] Re: [PATCH uq/master -v2 2/2] KVM, MCE, unpoison memory address across reboot

[Jan Kiszka]

On 2011-02-09 04:00, Huang Ying wrote:
> 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.

Yeah, saw this already during my test...

> 
> 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.

I just wondering what would be architecturally suboptimal if we simply
remapped on SIGBUS directly. Would save us at least the bookkeeping.

> 
> 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>
> ---
>  target-i386/kvm.c |   39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -508,6 +508,42 @@ static int kvm_get_supported_msrs(KVMSta
>      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);
> +
> +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);
> +    }
> +}
> +
> +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(KVMState *s)
>  {
>      uint64_t identity_base = 0xfffbc000;
> @@ -556,6 +592,7 @@ int kvm_arch_init(KVMState *s)
>          fprintf(stderr, "e820_add_entry() table is full\n");
>          return ret;
>      }
> +    qemu_register_reset(kvm_unpoison_all, NULL);
>  
>      return 0;
>  }
> @@ -1882,6 +1919,7 @@ int kvm_arch_on_sigbus_vcpu(CPUState *en
>                  hardware_memory_error();
>              }
>          }
> +        kvm_hwpoison_page_add(ram_addr);
>  
>          if (code == BUS_MCEERR_AR) {
>              /* Fake an Intel architectural Data Load SRAR UCR */
> @@ -1926,6 +1964,7 @@ int kvm_arch_on_sigbus(int code, void *a
>                      "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
> 
> 

Looks fine otherwise. Unless that simplification makes sense, I could
offer to include this into my MCE rework (there is some minor conflict).
If all goes well, that series should be posted during this week.

Jan

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