[PATCH] arm/arm64: KVM: send SIGBUS error to qemu
From: james.morse@arm.com (James Morse)
Date: 2017-03-23 15:07:08
Also in:
kvm, kvmarm, lkml
Hi Dongjiu Geng, On 23/03/17 13:01, Dongjiu Geng wrote:
when the pfn is KVM_PFN_ERR_HWPOISON, it indicates to send SIGBUS signal from KVM's fault-handling code to qemu, qemu can handle this signal according to the fault address.
I'm afraid I beat you to it on this one: https://www.spinics.net/lists/arm-kernel/msg568919.html (Are you the same gengdj who ask me to post that patch?: https://lkml.org/lkml/2017/3/5/187 ) We don't need upstream KVM to do this until either arm or arm64 has ARCH_SUPPORTS_MEMORY_FAILURE. Punit and Tyler have discovered problems with the way arm64's hugepage and hwpoison interact: https://www.spinics.net/lists/arm-kernel/msg568995.html Some comments on the differences:
quoted hunk ↗ jump to hunk
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c index 962616fd4ddd..1307ec400de3 100644 --- a/arch/arm/kvm/mmu.c +++ b/arch/arm/kvm/mmu.c@@ -1237,6 +1237,20 @@ 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, + struct task_struct *tsk) +{ + siginfo_t info; + + info.si_signo = SIGBUS; + info.si_errno = 0; + info.si_code = BUS_MCEERR_AR; + info.si_addr = (void __user *)address; + info.si_addr_lsb = PAGE_SHIFT;
Any version of this patch should handle hugepage for the sizes KVM uses in its stage2 mappings. By just passing PAGE_SHIFT you let the guest fault for each page that makes up the hugepage.
quoted hunk ↗ jump to hunk
+ + send_sig_info(SIGBUS, &info, tsk); +} + 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)@@ -1309,6 +1323,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, if (is_error_noslot_pfn(pfn)) return -EFAULT; + if (is_error_hwpoison_pfn(pfn)) { + kvm_send_hwpoison_signal(kvm_vcpu_gfn_to_hva(vcpu, gfn), + current); + return -EFAULT;
This will return -EFAULT from the KVM_RUN ioctl(). Is Qemu expected to know it should try again? This is indistinguishable from the is_error_noslot_pfn() error above. x86 returns 0 from this path, kvm_handle_bad_page() in arch/x86/kvm/mmu.c as the SIGBUS should arrive first. If the SIGBUS is handled the error has been resolved and Qemu can call KVM_RUN again. Returning an error and sending SIGBUS suggests there are two problems.
+ }
+
if (kvm_is_device_pfn(pfn)) {
mem_type = PAGE_S2_DEVICE;
flags |= KVM_S2PTE_FLAG_IS_IOMAP;Thanks, James