linux-kernel - Re: [PATCH v3 06/27] x86/cea: Export per CPU variable cea_exception

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Message-ID: <086b90a9-7e85-4c38-91d1-e70db2ee8355@intel.com>
Date: Tue, 1 Oct 2024 11:18:46 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Xin Li <xin@...or.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Cc: seanjc@...gle.com, pbonzini@...hat.com, corbet@....net,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, luto@...nel.org,
 peterz@...radead.org, andrew.cooper3@...rix.com
Subject: Re: [PATCH v3 06/27] x86/cea: Export per CPU variable
 cea_exception_stacks

On 10/1/24 10:51, Xin Li wrote:
...>> Also, what's the purpose of clearing GUEST_IA32_FRED_RSP[123] at
>> init_vmcs() time?  I would have thought that those values wouldn't
>> matter until the VMCS gets loaded at vmx_vcpu_load_vmcs() when they are
>> overwritten anyway.  Or, I could be just totally misunderstanding how
>> KVM consumes the VMCS. 🙂
> 
> I don't see any misunderstanding.  However we just do what the SDM
> claims, even it seems that it's not a must *logically*.
> 
> FRED spec says:
> The RESET state of each of the new MSRs is zero. INIT does not change
> the value of the new MSRs

Oh, sorry.  I was misreading the "HOST_" and "GUEST_" MSR prefixes.  I
thought the same VMCS field was being written at VMCS load *and* init
time (which it isn't).  Sorry for the noise.