linux-kernel - Re: [PATCH 04/21] KVM: x86/mmu: Allow non-zero value for non-present SPTE and removed SPTE

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Message-ID: <5ac647f6-84aa-40e5-8d67-112e38a48382@intel.com>
Date: Thu, 29 Feb 2024 21:55:04 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org
Cc: seanjc@...gle.com, michael.roth@....com, isaku.yamahata@...el.com,
 thomas.lendacky@....com, Binbin Wu <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH 04/21] KVM: x86/mmu: Allow non-zero value for non-present
 SPTE and removed SPTE

On 2/28/2024 7:20 AM, Paolo Bonzini wrote:
> From: Sean Christopherson <seanjc@...gle.com>
> 
> For TD guest, the current way to emulate MMIO doesn't work any more, as KVM
> is not able to access the private memory of TD guest and do the emulation.
> Instead, TD guest expects to receive #VE when it accesses the MMIO and then
> it can explicitly make hypercall to KVM to get the expected information.
> 
> To achieve this, the TDX module always enables "EPT-violation #VE" in the
> VMCS control.  And accordingly, for the MMIO spte for the shared GPA,
> 1. KVM needs to set "suppress #VE" bit for the non-present SPTE so that EPT
> violation happens on TD accessing MMIO range.  2. On EPT violation, KVM
> sets the MMIO spte to clear "suppress #VE" bit so the TD guest can receive
> the #VE instead of EPT misconfiguration unlike VMX case.  For the shared GPA
> that is not populated yet, EPT violation need to be triggered when TD guest
> accesses such shared GPA.  The non-present SPTE value for shared GPA should
> set "suppress #VE" bit.
> 
> Add "suppress #VE" bit (bit 63) to SHADOW_NONPRESENT_VALUE and
> REMOVED_SPTE.  Unconditionally set the "suppress #VE" bit (which is bit 63)
> for both AMD and Intel as: 1) AMD hardware doesn't use this bit when
> present bit is off; 2) for normal VMX guest, KVM never enables the
> "EPT-violation #VE" in VMCS control and "suppress #VE" bit is ignored by
> hardware.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Reviewed-by: Binbin Wu <binbin.wu@...ux.intel.com>
> Message-Id: <a99cb866897c7083430dce7f24c63b17d7121134.1705965635.git.isaku.yamahata@...el.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

+ 1 to the nit pointed by Yilun,

after that,

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>