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

Hi Punit,

On 17/03/17 15:06, Punit Agrawal wrote:

James Morse [off-list ref] writes:

quoted

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.

quoted

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

@@ -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);
+}

The changes look good to me. Though in essence as mentioned in the
commit log we are not doing anything different to x86 here. Worth moving
kvm_send_hwpoison_signal to an architecture agostic location and using
it from there?

I had an earlier version that did exactly that, but the x86 version always
reports PAGE_SHIFT as the si_addr_lsb value. I don't know enough about their
version of stage2 to know if that's a bug or an implementation detail, so I
chose not to copy it.

In any case, FWIW,

Reviewed-by: Punit Agrawal <redacted>

Thanks!

James