linux-kernel - Re: [PATCH v4 1/3] KVM: SVM: use vmsave/vmload for saving/restoring additional host state

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Date:   Tue, 2 Feb 2021 16:38:02 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Michael Roth <michael.roth@....com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v4 1/3] KVM: SVM: use vmsave/vmload for saving/restoring
 additional host state

One quick comment while it's on my mind, I'll give this a proper gander tomorrow.

On Tue, Feb 02, 2021, Michael Roth wrote:
> diff --git a/arch/x86/kvm/svm/svm_ops.h b/arch/x86/kvm/svm/svm_ops.h
> index 0c8377aee52c..c2a05f56c8e4 100644
> --- a/arch/x86/kvm/svm/svm_ops.h
> +++ b/arch/x86/kvm/svm/svm_ops.h
> @@ -56,4 +56,9 @@ static inline void vmsave(hpa_t pa)
>  	svm_asm1(vmsave, "a" (pa), "memory");
>  }
>  
> +static inline void vmload(hpa_t pa)

This needs to be 'unsigned long', using 'hpa_t' in vmsave() is wrong as the
instructions consume rAX based on effective address.  I wrote the function
comment for the vmsave() fix so that it applies to both VMSAVE and VMLOAD,
so this can be a simple fixup on application (assuming v5 isn't needed for
other reasons).

https://lkml.kernel.org/r/20210202223416.2702336-1-seanjc@google.com

> +{
> +	svm_asm1(vmload, "a" (pa), "memory");
> +}
> +
>  #endif /* __KVM_X86_SVM_OPS_H */
> -- 
> 2.25.1
>