linux-kernel - Re: [PATCH v2 2/3] KVM: x86: dump_vmcs should not conflate EFER and PAT presence in VMCS

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Message-ID: <m2zgztego1.fsf@dme.org>
Date:   Wed, 24 Feb 2021 13:31:10 +0000
From:   David Edmondson <dme@....org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
        Joerg Roedel <joro@...tes.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH v2 2/3] KVM: x86: dump_vmcs should not conflate EFER and
 PAT presence in VMCS

On Tuesday, 2021-02-23 at 14:58:29 -08, Sean Christopherson wrote:

> On Fri, Feb 19, 2021, David Edmondson wrote:
>> Show EFER and PAT based on their individual entry/exit controls.
>> 
>> Signed-off-by: David Edmondson <david.edmondson@...cle.com>
>> ---
>>  arch/x86/kvm/vmx/vmx.c | 19 ++++++++++---------
>>  1 file changed, 10 insertions(+), 9 deletions(-)
>> 
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index 818051c9fa10..25090e3683ca 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -5805,11 +5805,12 @@ void dump_vmcs(void)
>>  	vmx_dump_sel("LDTR:", GUEST_LDTR_SELECTOR);
>>  	vmx_dump_dtsel("IDTR:", GUEST_IDTR_LIMIT);
>>  	vmx_dump_sel("TR:  ", GUEST_TR_SELECTOR);
>> -	if ((vmexit_ctl & (VM_EXIT_SAVE_IA32_PAT | VM_EXIT_SAVE_IA32_EFER)) ||
>> -	    (vmentry_ctl & (VM_ENTRY_LOAD_IA32_PAT | VM_ENTRY_LOAD_IA32_EFER)))
>> -		pr_err("EFER =     0x%016llx  PAT = 0x%016llx\n",
>> -		       vmcs_read64(GUEST_IA32_EFER),
>> -		       vmcs_read64(GUEST_IA32_PAT));
>> +	if ((vmexit_ctl & VM_EXIT_SAVE_IA32_EFER) ||
>
> Not your code, and completely benign since VM_EXIT_SAVE is never set, but I
> don't like checking the VM_EXIT_SAVE_* flag as saving a field on VM-Exit has
> zero impact on whether VM-Entry succeeds or fails.  Same complaint on the PAT
> field.

Added to v3.

>> +	    (vmentry_ctl & VM_ENTRY_LOAD_IA32_EFER))
>> +		pr_err("EFER= 0x%016llx\n", vmcs_read64(GUEST_IA32_EFER));
>
> Tying into the previous patch, I think we should print both the effective EFER
> and vmcs.EFER.  The effective EFER is relevant for several consistency checks.
> Maybe something like this?
>
> 	pr_err("EFER= 0x%016llx  ", effective_efer);
> 	if (vmentry_ctl & VM_ENTRY_LOAD_IA32_EFER)
> 		pr_cont("vmcs.EFER= 0x%016llx\n", vmcs_read64(GUEST_IA32_EFER));
> 	else
> 		pr_cont("vmcs.EFER not loaded\n")

Added something similar, that makes it clear where the value came from,
in v3.

>> +	if ((vmexit_ctl & VM_EXIT_SAVE_IA32_PAT) ||
>> +	    (vmentry_ctl & VM_ENTRY_LOAD_IA32_PAT))
>> +		pr_err("PAT = 0x%016llx\n", vmcs_read64(GUEST_IA32_PAT));
>>  	pr_err("DebugCtl = 0x%016llx  DebugExceptions = 0x%016lx\n",
>>  	       vmcs_read64(GUEST_IA32_DEBUGCTL),
>>  	       vmcs_readl(GUEST_PENDING_DBG_EXCEPTIONS));
>> @@ -5846,10 +5847,10 @@ void dump_vmcs(void)
>>  	       vmcs_readl(HOST_IA32_SYSENTER_ESP),
>>  	       vmcs_read32(HOST_IA32_SYSENTER_CS),
>>  	       vmcs_readl(HOST_IA32_SYSENTER_EIP));
>> -	if (vmexit_ctl & (VM_EXIT_LOAD_IA32_PAT | VM_EXIT_LOAD_IA32_EFER))
>> -		pr_err("EFER = 0x%016llx  PAT = 0x%016llx\n",
>> -		       vmcs_read64(HOST_IA32_EFER),
>> -		       vmcs_read64(HOST_IA32_PAT));
>> +	if (vmexit_ctl & VM_EXIT_LOAD_IA32_EFER)
>> +		pr_err("EFER= 0x%016llx\n", vmcs_read64(HOST_IA32_EFER));
>> +	if (vmexit_ctl & VM_EXIT_LOAD_IA32_PAT)
>> +		pr_err("PAT = 0x%016llx\n", vmcs_read64(HOST_IA32_PAT));
>>  	if (cpu_has_load_perf_global_ctrl() &&
>>  	    vmexit_ctl & VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL)
>>  		pr_err("PerfGlobCtl = 0x%016llx\n",
>> -- 
>> 2.30.0
>> 

dme.
-- 
And the sign said: long haired freaky people need not apply.