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Date:   Thu, 2 Apr 2020 17:36:53 -0500
From:   Venu Busireddy <venu.busireddy@oracle.com>
To:     Ashish Kalra <Ashish.Kalra@amd.com>
Cc:     pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com,
        hpa@zytor.com, joro@8bytes.org, bp@suse.de,
        thomas.lendacky@amd.com, x86@kernel.org, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, rientjes@google.com,
        srutherford@google.com, luto@kernel.org, brijesh.singh@amd.com
Subject: Re: [PATCH v6 07/14] KVM: x86: Add AMD SEV specific Hypercall3
Message-ID: <20200402223653.GA659595@vbusired-dt>
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On 2020-03-30 06:21:52 +0000, Ashish Kalra wrote:
> From: Brijesh Singh <Brijesh.Singh@amd.com>
> 
> KVM hypercall framework relies on alternative framework to patch the
> VMCALL -> VMMCALL on AMD platform. If a hypercall is made before
> apply_alternative() is called then it defaults to VMCALL. The approach
> works fine on non SEV guest. A VMCALL would causes #UD, and hypervisor
                                              ^^^^^^
					      cause
> 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
                               ^^
			       which
> will be used by the SEV guest to notify encrypted pages to the hypervisor.
> 
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: x86@kernel.org
> Cc: kvm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>

Reviewed-by: Venu Busireddy <venu.busireddy@oracle.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);
> -- 
> 2.17.1
>