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Message-ID: <0ee32216-e285-406f-b20d-dd193b791d2b@intel.com>
Date: Wed, 8 Nov 2023 18:06:40 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Michal Luczaj <mhal@...x.co>,
Oliver Upton <oliver.upton@...ux.dev>,
Colton Lewis <coltonlewis@...gle.com>
Subject: Re: [PATCH v2 2/2] KVM: selftests: Add logic to detect if ioctl()
failed because VM was killed
On 11/8/2023 9:09 AM, Sean Christopherson wrote:
> Add yet another macro to the VM/vCPU ioctl() framework to detect when an
> ioctl() failed because KVM killed/bugged the VM, i.e. when there was
> nothing wrong with the ioctl() itself. If KVM kills a VM, e.g. by way of
> a failed KVM_BUG_ON(), all subsequent VM and vCPU ioctl()s will fail with
> -EIO, which can be quite misleading and ultimately waste user/developer
> time.
>
> Use KVM_CHECK_EXTENSION on KVM_CAP_USER_MEMORY to detect if the VM is
> dead and/or bug, as KVM doesn't provide a dedicated ioctl(). Using a
> heuristic is obviously less than ideal, but practically speaking the logic
> is bulletproof barring a KVM change, and any such change would arguably
> break userspace, e.g. if KVM returns something other than -EIO.
We hit similar issue when testing TDX VMs. Most failure of SEMCALL is
handled with a KVM_BUG_ON(), which leads to vm dead. Then the following
IOCTL from userspace (QEMU) and gets -EIO.
Can we return a new KVM_EXIT_VM_DEAD on KVM_REQ_VM_DEAD? and replace
-EIO with 0? yes, it's a ABI change. But I'm wondering if any userspace
relies on -EIO behavior for VM DEAD case.
> Without the detection, tearing down a bugged VM yields a cryptic failure
> when deleting memslots:
>
> ==== Test Assertion Failure ====
> lib/kvm_util.c:689: !ret
> pid=45131 tid=45131 errno=5 - Input/output error
> 1 0x00000000004036c3: __vm_mem_region_delete at kvm_util.c:689
> 2 0x00000000004042f0: kvm_vm_free at kvm_util.c:724 (discriminator 12)
> 3 0x0000000000402929: race_sync_regs at sync_regs_test.c:193
> 4 0x0000000000401cab: main at sync_regs_test.c:334 (discriminator 6)
> 5 0x0000000000416f13: __libc_start_call_main at libc-start.o:?
> 6 0x000000000041855f: __libc_start_main_impl at ??:?
> 7 0x0000000000401d40: _start at ??:?
> KVM_SET_USER_MEMORY_REGION failed, rc: -1 errno: 5 (Input/output error)
>
> Which morphs into a more pointed error message with the detection:
>
> ==== Test Assertion Failure ====
> lib/kvm_util.c:689: false
> pid=80347 tid=80347 errno=5 - Input/output error
> 1 0x00000000004039ab: __vm_mem_region_delete at kvm_util.c:689 (discriminator 5)
> 2 0x0000000000404660: kvm_vm_free at kvm_util.c:724 (discriminator 12)
> 3 0x0000000000402ac9: race_sync_regs at sync_regs_test.c:193
> 4 0x0000000000401cb7: main at sync_regs_test.c:334 (discriminator 6)
> 5 0x0000000000418263: __libc_start_call_main at libc-start.o:?
> 6 0x00000000004198af: __libc_start_main_impl at ??:?
> 7 0x0000000000401d90: _start at ??:?
> KVM killed/bugged the VM, check the kernel log for clues
>
> Suggested-by: Michal Luczaj <mhal@...x.co>
> Cc: Oliver Upton <oliver.upton@...ux.dev>
> Cc: Colton Lewis <coltonlewis@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
> .../selftests/kvm/include/kvm_util_base.h | 39 ++++++++++++++++---
> tools/testing/selftests/kvm/lib/kvm_util.c | 2 +-
> 2 files changed, 35 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> index 1f6193dc7d3a..c7717942ddbb 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> @@ -282,11 +282,40 @@ static __always_inline void static_assert_is_vm(struct kvm_vm *vm) { }
> kvm_do_ioctl((vm)->fd, cmd, arg); \
> })
>
> +/*
> + * Assert that a VM or vCPU ioctl() succeeded, with extra magic to detect if
> + * the ioctl() failed because KVM killed/bugged the VM. To detect a dead VM,
> + * probe KVM_CAP_USER_MEMORY, which (a) has been supported by KVM since before
> + * selftests existed and (b) should never outright fail, i.e. is supposed to
> + * return 0 or 1. If KVM kills a VM, KVM returns -EIO for all ioctl()s for the
> + * VM and its vCPUs, including KVM_CHECK_EXTENSION.
> + */
> +#define __TEST_ASSERT_VM_VCPU_IOCTL(cond, name, ret, vm) \
> +do { \
> + int __errno = errno; \
> + \
> + static_assert_is_vm(vm); \
> + \
> + if (cond) \
> + break; \
> + \
> + if (errno == EIO && \
> + __vm_ioctl(vm, KVM_CHECK_EXTENSION, (void *)KVM_CAP_USER_MEMORY) < 0) { \
> + TEST_ASSERT(errno == EIO, "KVM killed the VM, should return -EIO"); \
> + TEST_FAIL("KVM killed/bugged the VM, check the kernel log for clues"); \
> + } \
> + errno = __errno; \
> + TEST_ASSERT(cond, __KVM_IOCTL_ERROR(name, ret)); \
> +} while (0)
> +
> +#define TEST_ASSERT_VM_VCPU_IOCTL(cond, cmd, ret, vm) \
> + __TEST_ASSERT_VM_VCPU_IOCTL(cond, #cmd, ret, vm)
> +
> #define vm_ioctl(vm, cmd, arg) \
> ({ \
> int ret = __vm_ioctl(vm, cmd, arg); \
> \
> - TEST_ASSERT(!ret, __KVM_IOCTL_ERROR(#cmd, ret)); \
> + __TEST_ASSERT_VM_VCPU_IOCTL(!ret, #cmd, ret, vm); \
> })
>
> static __always_inline void static_assert_is_vcpu(struct kvm_vcpu *vcpu) { }
> @@ -301,7 +330,7 @@ static __always_inline void static_assert_is_vcpu(struct kvm_vcpu *vcpu) { }
> ({ \
> int ret = __vcpu_ioctl(vcpu, cmd, arg); \
> \
> - TEST_ASSERT(!ret, __KVM_IOCTL_ERROR(#cmd, ret)); \
> + __TEST_ASSERT_VM_VCPU_IOCTL(!ret, #cmd, ret, (vcpu)->vm); \
> })
>
> /*
> @@ -312,7 +341,7 @@ static inline int vm_check_cap(struct kvm_vm *vm, long cap)
> {
> int ret = __vm_ioctl(vm, KVM_CHECK_EXTENSION, (void *)cap);
>
> - TEST_ASSERT(ret >= 0, KVM_IOCTL_ERROR(KVM_CHECK_EXTENSION, ret));
> + TEST_ASSERT_VM_VCPU_IOCTL(ret >= 0, KVM_CHECK_EXTENSION, ret, vm);
> return ret;
> }
>
> @@ -371,7 +400,7 @@ static inline int vm_get_stats_fd(struct kvm_vm *vm)
> {
> int fd = __vm_ioctl(vm, KVM_GET_STATS_FD, NULL);
>
> - TEST_ASSERT(fd >= 0, KVM_IOCTL_ERROR(KVM_GET_STATS_FD, fd));
> + TEST_ASSERT_VM_VCPU_IOCTL(fd >= 0, KVM_GET_STATS_FD, fd, vm);
> return fd;
> }
>
> @@ -583,7 +612,7 @@ static inline int vcpu_get_stats_fd(struct kvm_vcpu *vcpu)
> {
> int fd = __vcpu_ioctl(vcpu, KVM_GET_STATS_FD, NULL);
>
> - TEST_ASSERT(fd >= 0, KVM_IOCTL_ERROR(KVM_GET_STATS_FD, fd));
> + TEST_ASSERT_VM_VCPU_IOCTL(fd >= 0, KVM_CHECK_EXTENSION, fd, vcpu->vm);
> return fd;
> }
>
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 7a8af1821f5d..c847f942cd38 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -1227,7 +1227,7 @@ struct kvm_vcpu *__vm_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id)
> vcpu->vm = vm;
> vcpu->id = vcpu_id;
> vcpu->fd = __vm_ioctl(vm, KVM_CREATE_VCPU, (void *)(unsigned long)vcpu_id);
> - TEST_ASSERT(vcpu->fd >= 0, KVM_IOCTL_ERROR(KVM_CREATE_VCPU, vcpu->fd));
> + TEST_ASSERT_VM_VCPU_IOCTL(vcpu->fd >= 0, KVM_CREATE_VCPU, vcpu->fd, vm);
>
> TEST_ASSERT(vcpu_mmap_sz() >= sizeof(*vcpu->run), "vcpu mmap size "
> "smaller than expected, vcpu_mmap_sz: %i expected_min: %zi",
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