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

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Date:   Mon, 26 Aug 2019 10:11:34 +0200
From:   Thomas Huth <thuth@...hat.com>
To:     Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Andrew Jones <drjones@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH] KVM: selftests: Detect max PA width from cpuid

On 26/08/2019 09.57, Peter Xu wrote:
> The dirty_log_test is failing on some old machines like Xeon E3-1220
> with tripple faults when writting to the tracked memory region:
> 
>   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
> 
> 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().
[...]
> 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;
>  }

You should also adjust the comment of the function. It currently says
"Never returns NULL". Not it can return NULL.

And maybe add a TEST_ASSERT() to the other callers instead, which do not
expect a NULL to be returned?

 Thomas