Re: [PATCH] KVM: selftests: Detect max PA width from cpuid

Vitaly Kuznetsov
2019-08-26T08:25:59Z

Peter Xu <peterx@redhat.com> writes:

> The dirty_log_test is failing on some old machines like Xeon E3-1220
> with tripple faults when writting to the tracked memory region:

s,writting,writing,

>
> Test iterations: 32, interval: 10 (ms)
> Testing guest mode: PA-bits:52, VA-bits:48, 4K pages
> guest physical test memory offset: 0x7fbffef000
> ==== Test Assertion Failure ====
> dirty_log_test.c:138: false
> pid=6137 tid=6139 - Success
> 1 0x0000000000401ca1: vcpu_worker at dirty_log_test.c:138
> 2 0x00007f3dd9e392dd: ?? ??:0
> 3 0x00007f3dd9b6a132: ?? ??:0
> Invalid guest sync status: exit_reason=SHUTDOWN
>

This patch breaks on my AMD machine with

# cpuid -1 -l 0x80000008
CPU:
Physical Address and Linear Address Size (0x80000008/eax):
maximum physical address bits = 0x30 (48)
maximum linear (virtual) address bits = 0x30 (48)
maximum guest physical address bits = 0x0 (0)

Pre-patch:

# ./dirty_log_test
Test iterations: 32, interval: 10 (ms)
Testing guest mode: PA-bits:52, VA-bits:48, 4K pages
guest physical test memory offset: 0x7fbffef000
Dirtied 139264 pages
Total bits checked: dirty (135251), clear (7991709), track_next (29789)

Post-patch:

# ./dirty_log_test
Test iterations: 32, interval: 10 (ms)
Testing guest mode: PA-bits:52, VA-bits:48, 4K pages
Supported guest physical address width: 48
guest physical test memory offset: 0xffffbffef000
==== Test Assertion Failure ====
dirty_log_test.c:141: false
pid=77983 tid=77985 - Success
1 0x0000000000401d12: vcpu_worker at dirty_log_test.c:138
2 0x00007f636374358d: ?? ??:0
3 0x00007f63636726a2: ?? ??:0
Invalid guest sync status: exit_reason=SHUTDOWN

> It's because previously we moved the testing memory region from a
> static place (1G) to the top of the system's physical address space,
> meanwhile we stick to 39 bits PA for all the x86_64 machines. That's
> not true for machines like Xeon E3-1220 where it only supports 36.
>
> Let's unbreak this test by dynamically detect PA width from CPUID
> 0x80000008. Meanwhile, even allow kvm_get_supported_cpuid_index() to
> fail. I don't know whether that could be useful because I think
> 0x80000008 should be there for all x86_64 hosts, but I also think it's
> not really helpful to assert in the kvm_get_supported_cpuid_index().
>
> Fixes: b442324b581556e
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Andrew Jones <drjones@redhat.com>
> CC: Radim Krčmář <rkrcmar@redhat.com>
> CC: Thomas Huth <thuth@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> tools/testing/selftests/kvm/dirty_log_test.c | 22 +++++++++++++------
> .../selftests/kvm/lib/x86_64/processor.c | 3 ---
> 2 files changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
> index ceb52b952637..111592f3a1d7 100644
> --- a/tools/testing/selftests/kvm/dirty_log_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_test.c
> @@ -274,18 +274,26 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
> DEBUG("Testing guest mode: %s\n", vm_guest_mode_string(mode));
>
> #ifdef __x86_64__
> - /*
> - * FIXME
> - * The x86_64 kvm selftests framework currently only supports a
> - * single PML4 which restricts the number of physical address
> - * bits we can change to 39.
> - */
> - guest_pa_bits = 39;
> + {
> + struct kvm_cpuid_entry2 *entry;
> +
> + entry = kvm_get_supported_cpuid_entry(0x80000008);
> + /*
> + * Supported PA width can be smaller than 52 even if
> + * we're with VM_MODE_P52V48_4K mode. Fetch it from
> + * the host to update the default value (SDM 4.1.4).
> + */
> + if (entry)
> + guest_pa_bits = entry->eax & 0xff;
> + else
> + guest_pa_bits = 32;
> + }
> #endif
> #ifdef __aarch64__
> if (guest_pa_bits != 40)
> type = KVM_VM_TYPE_ARM_IPA_SIZE(guest_pa_bits);
> #endif
> + printf("Supported guest physical address width: %d\n", guest_pa_bits);
> max_gfn = (1ul << (guest_pa_bits - guest_page_shift)) - 1;
> guest_page_size = (1ul << guest_page_shift);
> /*
> diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> index 6cb34a0fa200..9de2fd310ac8 100644
> --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
> +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> @@ -760,9 +760,6 @@ kvm_get_supported_cpuid_index(uint32_t function, uint32_t index)
> break;
> }
> }
> -
> - TEST_ASSERT(entry, "Guest CPUID entry not found: (EAX=%x, ECX=%x).",
> - function, index);
> return entry;
> }

--
Vitaly