linux-kernel - Re: [PATCH v5 06/15] x86/sev: Drop redundant and potentially misleading 'sev

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Message-ID: <8f1fa7e0-b940-6d1d-1a74-11014901fc0d@redhat.com>
Date:   Thu, 22 Apr 2021 14:05:46 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v5 06/15] x86/sev: Drop redundant and potentially
 misleading 'sev_enabled'

On 22/04/21 04:11, Sean Christopherson wrote:
> Drop the sev_enabled flag and switch its one user over to sev_active().
> sev_enabled was made redundant with the introduction of sev_status in
> commit b57de6cd1639 ("x86/sev-es: Add SEV-ES Feature Detection").
> sev_enabled and sev_active() are guaranteed to be equivalent, as each is
> true iff 'sev_status & MSR_AMD64_SEV_ENABLED' is true, and are only ever
> written in tandem (ignoring compressed boot's version of sev_status).
> 
> Removing sev_enabled avoids confusion over whether it refers to the guest
> or the host, and will also allow KVM to usurp "sev_enabled" for its own
> purposes.
> 
> No functional change intended.
> 
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> Reviewed-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Boris or another x86 maintainer, can you ack this small patch?  We would 
like to use sev_enabled as a static variable in KVM.

Paolo

> ---
>   arch/x86/include/asm/mem_encrypt.h |  1 -
>   arch/x86/mm/mem_encrypt.c          | 12 +++++-------
>   arch/x86/mm/mem_encrypt_identity.c |  1 -
>   3 files changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index 31c4df123aa0..9c80c68d75b5 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -20,7 +20,6 @@
>   
>   extern u64 sme_me_mask;
>   extern u64 sev_status;
> -extern bool sev_enabled;
>   
>   void sme_encrypt_execute(unsigned long encrypted_kernel_vaddr,
>   			 unsigned long decrypted_kernel_vaddr,
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 4b01f7dbaf30..be384d8d0543 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -44,8 +44,6 @@ EXPORT_SYMBOL(sme_me_mask);
>   DEFINE_STATIC_KEY_FALSE(sev_enable_key);
>   EXPORT_SYMBOL_GPL(sev_enable_key);
>   
> -bool sev_enabled __section(".data");
> -
>   /* Buffer used for early in-place encryption by BSP, no locking needed */
>   static char sme_early_buffer[PAGE_SIZE] __initdata __aligned(PAGE_SIZE);
>   
> @@ -373,15 +371,15 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size)
>    * up under SME the trampoline area cannot be encrypted, whereas under SEV
>    * the trampoline area must be encrypted.
>    */
> -bool sme_active(void)
> -{
> -	return sme_me_mask && !sev_enabled;
> -}
> -
>   bool sev_active(void)
>   {
>   	return sev_status & MSR_AMD64_SEV_ENABLED;
>   }
> +
> +bool sme_active(void)
> +{
> +	return sme_me_mask && !sev_active();
> +}
>   EXPORT_SYMBOL_GPL(sev_active);
>   
>   /* Needs to be called from non-instrumentable code */
> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> index 6c5eb6f3f14f..0c2759b7f03a 100644
> --- a/arch/x86/mm/mem_encrypt_identity.c
> +++ b/arch/x86/mm/mem_encrypt_identity.c
> @@ -545,7 +545,6 @@ void __init sme_enable(struct boot_params *bp)
>   
>   		/* SEV state cannot be controlled by a command line option */
>   		sme_me_mask = me_mask;
> -		sev_enabled = true;
>   		physical_mask &= ~sme_me_mask;
>   		return;
>   	}
>