linux-kernel - Re: [PATCH 0/7] KVM: TDX: TD vcpu enter/exit

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Message-ID: <86d71f0c-6859-477a-88a2-416e46847f2f@linux.intel.com>
Date: Mon, 25 Nov 2024 09:25:56 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: seanjc@...gle.com, Adrian Hunter <adrian.hunter@...el.com>,
 pbonzini@...hat.com
Cc: dave.hansen@...ux.intel.com, kvm@...r.kernel.org,
 rick.p.edgecombe@...el.com, kai.huang@...el.com, reinette.chatre@...el.com,
 xiaoyao.li@...el.com, tony.lindgren@...ux.intel.com, dmatlack@...gle.com,
 isaku.yamahata@...el.com, nik.borisov@...e.com,
 linux-kernel@...r.kernel.org, x86@...nel.org, yan.y.zhao@...el.com,
 chao.gao@...el.com, weijiang.yang@...el.com
Subject: Re: [PATCH 0/7] KVM: TDX: TD vcpu enter/exit




On 11/22/2024 4:14 AM, Adrian Hunter wrote:
[...]
>    - tdx_vcpu_enter_exit() calls guest_state_enter_irqoff()
>      and guest_state_exit_irqoff() which comments say should be
>      called from non-instrumentable code but noinst was removed
>      at Sean's suggestion:
>    	https://lore.kernel.org/all/Zg8tJspL9uBmMZFO@google.com/
>      noinstr is also needed to retain NMI-blocking by avoiding
>      instrumented code that leads to an IRET which unblocks NMIs.
>      A later patch set will deal with NMI VM-exits.
>
In https://lore.kernel.org/all/Zg8tJspL9uBmMZFO@google.com, Sean mentioned:
"The reason the VM-Enter flows for VMX and SVM need to be noinstr is they do things
like load the guest's CR2, and handle NMI VM-Exits with NMIs blocks.  None of
that applies to TDX.  Either that, or there are some massive bugs lurking due to
missing code."

I don't understand why handle NMI VM-Exits with NMIs blocks doesn't apply to
TDX.  IIUIC, similar to VMX, TDX also needs to handle the NMI VM-exit in the
noinstr section to avoid the unblock of NMIs due to instrumentation-induced
fault.