linux-kernel - Re: [PATCH] KVM: selftests: restore special vmmcall code layout needed by the harness

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Date:   Thu, 01 Dec 2022 15:48:58 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: selftests: restore special vmmcall code layout
 needed by the harness

On Thu, 2022-12-01 at 10:28 +0100, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@...gle.com> writes:
> 
> > On Wed, Nov 30, 2022, Paolo Bonzini wrote:
> > > Commit 8fda37cf3d41 ("KVM: selftests: Stuff RAX/RCX with 'safe' values
> > > in vmmcall()/vmcall()", 2022-11-21) broke the svm_nested_soft_inject_test
> > > because it placed a "pop rbp" instruction after vmmcall.  While this is
> > > correct and mimics what is done in the VMX case, this particular test
> > > expects a ud2 instruction right after the vmmcall, so that it can skip
> > > over it in the L1 part of the test.
> > > 
> > > Inline a suitably-modified version of vmmcall() to restore the
> > > functionality of the test.
> > > 
> > > Fixes: 8fda37cf3d41 ("KVM: selftests: Stuff RAX/RCX with 'safe' values in vmmcall()/vmcall()"
> > > Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
> > > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > > ---
> > 
> > We really, really need to save/restore guest GPRs in L1 when handling exits from L2.
> 
> +1, the amount of stuff we do to workaround the shortcoming (and time
> we waste debugging) is getting ridiculously high. 
> 
> > For now,
> > 
> > Reviewed-by: Sean Christopherson <seanjc@...gle.com>
> > 
> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> 

I didn't notice this fix and also found this issue.

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky