linux-kernel - Re: [PATCH v6 07/14] KVM: x86: Add AMD SEV specific Hypercall3

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Date:   Thu, 2 Apr 2020 16:54:35 -0700
From:   Krish Sadhukhan <krish.sadhukhan@...cle.com>
To:     Ashish Kalra <Ashish.Kalra@....com>, pbonzini@...hat.com
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        joro@...tes.org, bp@...e.de, thomas.lendacky@....com,
        x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rientjes@...gle.com, srutherford@...gle.com, luto@...nel.org,
        brijesh.singh@....com
Subject: Re: [PATCH v6 07/14] KVM: x86: Add AMD SEV specific Hypercall3


On 3/29/20 11:21 PM, Ashish Kalra wrote:
> From: Brijesh Singh <Brijesh.Singh@....com>
>
> KVM hypercall framework relies on alternative framework to patch the
> VMCALL -> VMMCALL on AMD platform. If a hypercall is made before
> apply_alternative()

s/apply_alternative/apply_alternatives/
> is called then it defaults to VMCALL. The approach
> works fine on non SEV guest. A VMCALL would causes #UD, and hypervisor
> will be able to decode the instruction and do the right things. But
> when SEV is active, guest memory is encrypted with guest key and
> hypervisor will not be able to decode the instruction bytes.
>
> Add SEV specific hypercall3, it unconditionally uses VMMCALL. The hypercall
> will be used by the SEV guest to notify encrypted pages to the hypervisor.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: "Radim Krčmář" <rkrcmar@...hat.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: x86@...nel.org
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> ---
>   arch/x86/include/asm/kvm_para.h | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 9b4df6eaa11a..6c09255633a4 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -84,6 +84,18 @@ static inline long kvm_hypercall4(unsigned int nr, unsigned long p1,
>   	return ret;
>   }
>   
> +static inline long kvm_sev_hypercall3(unsigned int nr, unsigned long p1,
> +				      unsigned long p2, unsigned long p3)
> +{
> +	long ret;
> +
> +	asm volatile("vmmcall"
> +		     : "=a"(ret)
> +		     : "a"(nr), "b"(p1), "c"(p2), "d"(p3)
> +		     : "memory");
> +	return ret;
> +}
> +
>   #ifdef CONFIG_KVM_GUEST
>   bool kvm_para_available(void);
>   unsigned int kvm_arch_para_features(void);
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@...cle.com>