linux-kernel - Re: [PATCH 7/7] KVM: VMX: Introduce test mode related to EPT violation VE

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Date: Fri, 17 May 2024 19:09:48 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [PATCH 7/7] KVM: VMX: Introduce test mode related to EPT
 violation VE

On 5/17/24 18:38, Sean Christopherson wrote:
>>> I've hit this three times now when running KVM-Unit-Tests (I'm pretty sure it's
>>> the EPT test, unsurprisingly).  And unless I screwed up my testing, I verified it
>>> still fires with Isaku's fix[*], though I'm suddenly having problems repro'ing.
>>>
>>> I'll update tomorrow as to whether I botched my testing of Isaku's fix, or if
>>> there's another bug lurking.
>>>
>>> https://lore.kernel.org/all/20240515173209.GD168153@ls.amr.corp.intel.com
>> I cannot reproduce it on a Skylake (Xeon Gold 5120), with or without Isaku's
>> fix, with either ./runtests.sh or your reproducer line.
>>
>> However I can reproduce it only if eptad=0 and with the following line:
>>
>> ./x86/run x86/vmx.flat -smp 1 -cpu max,host-phys-bits,+vmx -m 2560 \
>>    -append 'ept_access_test_not_present ept_access_test_read_only'
>
> FWIW, I tried that on RPL, still no failure.

Ok, so it does look like a CPU issue.  Even with the fixes you 
identified, I don't see any other solution than adding scary text in 
Kconfig, defaulting it to "n", and adding an also-very-scary 
pr_err_once("...") the first time VMPTRLD is executed with 
CONFIG_KVM_INTEL_PROVE_VE.

Paolo