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From: Sean Christopherson <seanjc@google.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-coco@lists.linux.dev, Joerg Roedel <jroedel@suse.de>
Subject: Re: [PATCH v2 1/4] KVM: SVM: Get rid of *ghcb_msr_bits() functions
Date: Wed, 1 Sep 2021 21:31:52 +0000	[thread overview]
Message-ID: <YS/xSIvhS5GySXlQ@google.com> (raw)
In-Reply-To: <YS/sqmgbS6ACRfSD@google.com>

On Wed, Sep 01, 2021, Sean Christopherson wrote:
> > -static u64 get_ghcb_msr_bits(struct vcpu_svm *svm, u64 mask, unsigned int pos)
> > -{
> > -	return (svm->vmcb->control.ghcb_gpa >> pos) & mask;
> > +	msr  = GHCB_MSR_CPUID_RESP;
> > +	msr |= (reg & GHCB_MSR_CPUID_REG_MASK) << GHCB_MSR_CPUID_REG_POS;
> > +	msr |= (value & GHCB_MSR_CPUID_VALUE_MASK) << GHCB_MSR_CPUID_VALUE_POS;
> > +
> > +	svm->vmcb->control.ghcb_gpa = msr;
> 
> I would rather have the get/set pairs be roughly symmetric, i.e. both functions
> or both macros, and both work on svm->vmcb->control.ghcb_gpa or both be purely
> functional (that may not be the correct word).
> 
> I don't have a strong preference on function vs. macro.  But for the second one,
> my preference would be to have the helper generate the value as opposed to taken
> and filling a pointer, e.g. to yield something like:
> 
> 		cpuid_reg = GHCB_MSR_CPUID_REG(control->ghcb_gpa);
> 
> 		if (cpuid_reg == 0)
> 			cpuid_value = vcpu->arch.regs[VCPU_REGS_RAX];
> 		else if (cpuid_reg == 1)
> 			cpuid_value = vcpu->arch.regs[VCPU_REGS_RBX];
> 		else if (cpuid_reg == 2)
> 			cpuid_value = vcpu->arch.regs[VCPU_REGS_RCX];
> 		else
> 			cpuid_value = vcpu->arch.regs[VCPU_REGS_RDX];
> 
> 		control->ghcb_gpa = MAKE_GHCB_MSR_RESP(cpuid_reg, cpuid_value);
> 
> 
> The advantage is that it's obvious from the code that control->ghcb_gpa is being
> read _and_ written.

Ah, but in the next path I see there's the existing ghcb_set_sw_exit_info_2().
Hrm.  I think I still prefer open coding "control->ghcb_gpa = ..." with the right
hand side being a macro.  That would gel with the INFO_REQ, e.g.

	case GHCB_MSR_SEV_INFO_REQ:
		control->ghcb_gpa = GHCB_MSR_SEV_INFO(GHCB_VERSION_MAX,
						      GHCB_VERSION_MIN,
						      sev_enc_bit));
		break;

and drop set_ghcb_msr() altogether.

Side topic, what about renaming control->ghcb_gpa => control->ghcb_msr so that
the code for the MSR protocol is a bit more self-documenting?  The APM defines
the field as "Guest physical address of GHCB", so it's not exactly prescribing a
specific name.

  reply	other threads:[~2021-09-01 21:31 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-22 11:52 [PATCH v2 0/4] KVM: SVM: Add initial GHCB protocol version 2 support Joerg Roedel
2021-07-22 11:52 ` [PATCH v2 1/4] KVM: SVM: Get rid of *ghcb_msr_bits() functions Joerg Roedel
2021-09-01 21:12   ` Sean Christopherson
2021-09-01 21:31     ` Sean Christopherson [this message]
2021-09-09 13:22       ` Joerg Roedel
2021-09-09 13:32     ` Joerg Roedel
2021-09-20 16:10       ` Sean Christopherson
2021-07-22 11:52 ` [PATCH v2 2/4] KVM: SVM: Add support to handle AP reset MSR protocol Joerg Roedel
2021-09-01 21:45   ` Sean Christopherson
2021-07-22 11:52 ` [PATCH v2 3/4] KVM: SVM: Add support for Hypervisor Feature support " Joerg Roedel
2021-07-22 12:01   ` [PATCH v2.1 " Joerg Roedel
2021-09-01 22:41     ` Sean Christopherson
2021-07-22 11:52 ` [PATCH v2 4/4] KVM: SVM: Increase supported GHCB protocol version Joerg Roedel

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