Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[gengdongjiu <gengdj.1984@gmail.com>]

Hi James,
   thanks for the patch, have you consider to told Qemu or KVM tools
the reason for this bus error(SEA/SEI)?

when Qemu or KVM tools get this SIGBUS signal, it do not know receive
this SIGBUS due to SEA or SEI.
OR KVM only send this SIGBUS when encounter SEA? if so, for the SEI
case, how to let Qemu simulate to generate CPER for guest OS SEI.


2017-03-16 0:07 GMT+08:00 James Morse <james.morse@arm.com>:
> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications for
> broken memory can call memory_failure() in mm/memory-failure.c to deliver
> SIGBUS to any user space process using the page, and notify all the
> in-kernel users.
>
> If the page corresponded with guest memory, KVM will unmap this page
> from its stage2 page tables. The user space process that allocated
> this memory may have never touched this page in which case it may not
> be mapped meaning SIGBUS won't be delivered.
>
> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
> comes to process the stage2 fault.
>
> Do as x86 does, and deliver the SIGBUS when we discover
> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
> as this matches the user space mapping size.
>
> Signed-off-by: James Morse <james.morse@arm.com>
> CC: gengdongjiu <gengdj.1984@gmail.com>
> ---
>  Without this patch both kvmtool and Qemu exit as the KVM_RUN ioctl() returns
>  EFAULT.
>  QEMU: error: kvm run failed Bad address
>  LVKM: KVM_RUN failed: Bad address
>
>  With this patch both kvmtool and Qemu receive SIGBUS ... and then exit.
>  In the future Qemu can use this signal to notify the guest, for more details
>  see hwpoison[1].
>
>  [0] https://www.spinics.net/lists/arm-kernel/msg560009.html
>  [1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/vm/hwpoison.txt
>
>
>  arch/arm/kvm/mmu.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 962616fd4ddd..9d1aa294e88f 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -20,8 +20,10 @@
>  #include <linux/kvm_host.h>
>  #include <linux/io.h>
>  #include <linux/hugetlb.h>
> +#include <linux/sched/signal.h>
>  #include <trace/events/kvm.h>
>  #include <asm/pgalloc.h>
> +#include <asm/siginfo.h>
>  #include <asm/cacheflush.h>
>  #include <asm/kvm_arm.h>
>  #include <asm/kvm_mmu.h>
> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct kvm_vcpu *vcpu, kvm_pfn_t pfn,
>         __coherent_cache_guest_page(vcpu, pfn, size);
>  }
>
> +static void kvm_send_hwpoison_signal(unsigned long address, bool hugetlb)
> +{
> +       siginfo_t info;
> +
> +       info.si_signo   = SIGBUS;
> +       info.si_errno   = 0;
> +       info.si_code    = BUS_MCEERR_AR;
> +       info.si_addr    = (void __user *)address;
> +
> +       if (hugetlb)
> +               info.si_addr_lsb = PMD_SHIFT;
> +       else
> +               info.si_addr_lsb = PAGE_SHIFT;
> +
> +       send_sig_info(SIGBUS, &info, current);
> +}
> +
>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>                           struct kvm_memory_slot *memslot, unsigned long hva,
>                           unsigned long fault_status)
> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>         smp_rmb();
>
>         pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);
> +       if (pfn == KVM_PFN_ERR_HWPOISON) {
> +               kvm_send_hwpoison_signal(hva, hugetlb);
> +               return 0;
> +       }
>         if (is_error_noslot_pfn(pfn))
>                 return -EFAULT;
>
> --
> 2.10.1
>