linux-kernel - Re: [PATCH v2 2/2] KVM:SVM: Update cr3_lm_rsvd

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Message-ID: <f9910665-8330-6db6-ee0a-2db9a69d6c95@redhat.com>
Date:   Fri, 13 Nov 2020 12:30:57 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Babu Moger <babu.moger@....com>
Cc:     junaids@...gle.com, wanpengli@...cent.com, kvm@...r.kernel.org,
        joro@...tes.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        sean.j.christopherson@...el.com, mingo@...hat.com, bp@...en8.de,
        hpa@...or.com, tglx@...utronix.de, vkuznets@...hat.com,
        jmattson@...gle.com
Subject: Re: [PATCH v2 2/2] KVM:SVM: Update cr3_lm_rsvd_bits for AMD SEV
 guests

On 12/11/20 23:18, Babu Moger wrote:
> +	/*
> +	 * For sev guests, update the cr3_lm_rsvd_bits to mask the memory
> +	 * encryption bit from reserved bits
> +	 */

Say why in the comment, don't repeat what the code already says (ok, 
technically the code didn't say that CPUID[0x8000001F].ebx hosts the 
memory encryption bit).  I changed this to:

/* For sev guests, the memory encryption bit is not reserved in CR3.  */

and queued the patches,

Paolo

> +	if (sev_guest(vcpu->kvm)) {
> +		best = kvm_find_cpuid_entry(vcpu, 0x8000001F, 0);
> +		if (best)
> +			vcpu->arch.cr3_lm_rsvd_bits &= ~(1UL << (best->ebx & 0x3f));
> +	}
> +