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

[Jan Kiszka]

Am 13.01.2011 09:34, 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.
> 
> 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 <address@hidden>
> ---
>  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)

Minor nit: This can be static now.

> +{
> +    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);
> +

To be removed if kvm_unpoison_all is static.

>  #endif
>  int kvm_set_ioeventfd_mmio_long(int fd, uint32_t adr, uint32_t val, bool 
> assign);
>  
> 

As indicated, I'm sitting on lots of fixes and refactorings of the MCE
user space code. How do you test your patches? Any suggestions how to do
this efficiently would be warmly welcome.

Thanks,
Jan

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