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Date:   Fri, 18 Sep 2020 09:56:51 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Krish Sadhukhan <krish.sadhukhan@oracle.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     kvm@vger.kernel.org, pbonzini@redhat.com, jmattson@google.com,
        tglx@linutronix.de, mingo@redhat.com, x86@kernel.org,
        sean.j.christopherson@intel.com, vkuznets@redhat.com,
        wanpengli@tencent.com, joro@8bytes.org,
        dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org,
        linux-kernel@vger.kernel.org, hpa@zytor.com
Subject: Re: [PATCH 3/3 v4] KVM: SVM: Don't flush cache if hardware enforces
 cache coherency across encryption domains
Message-ID: <20200918075651.GC6585@zn.tnic>
References: <20200917212038.5090-1-krish.sadhukhan@oracle.com>
 <20200917212038.5090-4-krish.sadhukhan@oracle.com>
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In-Reply-To: <20200917212038.5090-4-krish.sadhukhan@oracle.com>
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On Thu, Sep 17, 2020 at 09:20:38PM +0000, Krish Sadhukhan wrote:
> In some hardware implementations, coherency between the encrypted and
> unencrypted mappings of the same physical page in a VM is enforced. In such a
> system, it is not required for software to flush the VM's page from all CPU
> caches in the system prior to changing the value of the C-bit for the page.
> 
> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> ---
>  arch/x86/kvm/svm/sev.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 7bf7bf734979..3c9a45efdd4d 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -384,7 +384,8 @@ static void sev_clflush_pages(struct page *pages[], unsigned long npages)
>  	uint8_t *page_virtual;
>  	unsigned long i;
>  
> -	if (npages == 0 || pages == NULL)
> +	if (this_cpu_has(X86_FEATURE_SME_COHERENT) || npages == 0 ||
> +	    pages == NULL)
>  		return;
>  
>  	for (i = 0; i < npages; i++) {
> -- 

Took the first two, Paolo lemme know if I should route this one through
tip too.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette