From: Oliver Upton <oliver.upton@linux.dev>
To: Andrei Vagin <avagin@gmail.com>
Cc: linux-kernel@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org
Subject: Re: [PATCH] selftests/kvm/x86_64: set rax before vmcall
Date: Fri, 29 Jul 2022 19:12:20 +0000 [thread overview]
Message-ID: <YuQxFDupaZuyUMmP@google.com> (raw)
In-Reply-To: <20220628193011.55403-1-avagin@gmail.com>
Hi Andrei,
On Tue, Jun 28, 2022 at 12:30:11PM -0700, Andrei Vagin wrote:
> kvm_hypercall has to place the hypercall number in rax.
>
> Trace events show that kvm_pv_test doesn't work properly:
> kvm_pv_test-53132: kvm_hypercall: nr 0x0 a0 0x0 a1 0x0 a2 0x0 a3 0x0
> kvm_pv_test-53132: kvm_hypercall: nr 0x0 a0 0x0 a1 0x0 a2 0x0 a3 0x0
> kvm_pv_test-53132: kvm_hypercall: nr 0x0 a0 0x0 a1 0x0 a2 0x0 a3 0x0
>
> With this change, it starts working as expected:
> kvm_pv_test-54285: kvm_hypercall: nr 0x5 a0 0x0 a1 0x0 a2 0x0 a3 0x0
> kvm_pv_test-54285: kvm_hypercall: nr 0xa a0 0x0 a1 0x0 a2 0x0 a3 0x0
> kvm_pv_test-54285: kvm_hypercall: nr 0xb a0 0x0 a1 0x0 a2 0x0 a3 0x0
>
> Signed-off-by: Andrei Vagin <avagin@gmail.com>
> ---
Good find, this is a rather silly bug. May I suggest the following for
the changelog to better describe the problem (and blame the original
commit):
KVM: selftests: Actually pass function in %rax when calling hypercall
The KVM hypercall ABI requires the caller to pass the hypercall function
number via %rax. Unfortunately, kvm_hypercall() in selftests falls
short and doesn't set the value of %rax.
In turn, trace events show that kvm_pv_test doesn't work properly:
kvm_pv_test-53132: kvm_hypercall: nr 0x0 a0 0x0 a1 0x0 a2 0x0 a3 0x0
kvm_pv_test-53132: kvm_hypercall: nr 0x0 a0 0x0 a1 0x0 a2 0x0 a3 0x0
kvm_pv_test-53132: kvm_hypercall: nr 0x0 a0 0x0 a1 0x0 a2 0x0 a3 0x0
Fix the issue by taking the function number as an input operand to %rax.
Fixes: ac4a4d6de22e ("selftests: kvm: test enforcement of paravirtual cpuid features")
--
Thanks,
Oliver
prev parent reply other threads:[~2022-07-29 19:12 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-28 19:30 [PATCH] selftests/kvm/x86_64: set rax before vmcall Andrei Vagin
2022-07-29 19:12 ` Oliver Upton [this message]
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