[PATCH] arm/arm64: KVM: send SIGBUS error to qemu

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.

Signed-off-by: Dongjiu Geng <redacted>
---
 arch/arm/kvm/mmu.c       | 20 ++++++++++++++++++++
 include/linux/kvm_host.h |  5 +++++
 2 files changed, 25 insertions(+)

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;
+
+	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;
+	}
+
 	if (kvm_is_device_pfn(pfn)) {
 		mem_type = PAGE_S2_DEVICE;
 		flags |= KVM_S2PTE_FLAG_IS_IOMAP;

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 2c14ad9809da..610ded9ebe9b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h

@@ -91,6 +91,11 @@ static inline bool is_noslot_pfn(kvm_pfn_t pfn)
 {
 	return pfn == KVM_PFN_NOSLOT;
 }
+/* hwpoison pfn indicates that it needs to send SIGBUS */
+static inline bool is_error_hwpoison_pfn(kvm_pfn_t pfn)
+{
+	return pfn == KVM_PFN_ERR_HWPOISON;
+}
 
 /*
  * architectures with KVM_HVA_ERR_BAD other than PAGE_OFFSET (e.g. s390)

-- 
2.11.0

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:

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.

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

Hi James,
   thanks for your review.

On 2017/3/23 23:06, James Morse wrote:

Hi Dongjiu Geng,

On 23/03/17 13:01, Dongjiu Geng wrote:

quoted

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 )

Oh, yes, it is me. recently I do not check my gmail and think you are not reply mail.
it is great that you upstream this patch.

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

  ok, thanks James. do you know when the arm or arm64 will have ARCH_SUPPORTS_MEMORY_FAILURE?

Some comments on the differences:

quoted

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

+
+	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.

  thanks for that. I think your Statement is reasonable.

quoted

+	}
+
 	if (kvm_is_device_pfn(pfn)) {
 		mem_type = PAGE_S2_DEVICE;
 		flags |= KVM_S2PTE_FLAG_IS_IOMAP;

Thanks,

James


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