linux-kernel - Re: [PATCH] KVM: x86/mmu: Embed direct bits into gpa for KVM_PRE_FAULT

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Message-ID: <58cf64a2c4a085099bb801e6c3a966b97bc182e3.camel@intel.com>
Date: Thu, 12 Jun 2025 18:50:48 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Zhao, Yan Y" <yan.y.zhao@...el.com>
CC: "seanjc@...gle.com" <seanjc@...gle.com>, "Huang, Kai"
	<kai.huang@...el.com>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>, "Chatre,
 Reinette" <reinette.chatre@...el.com>, "Hunter, Adrian"
	<adrian.hunter@...el.com>, "tony.lindgren@...ux.intel.com"
	<tony.lindgren@...ux.intel.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86/mmu: Embed direct bits into gpa for
 KVM_PRE_FAULT_MEMORY

On Thu, 2025-06-12 at 15:19 +0800, Yan Zhao wrote:
> > TDX isn't setting PFERR_WRITE_MASK or PFERR_PRESENT_MASK in the error_code
> > passed into the fault handler. So page_fault_can_be_fast() should return
> > false
> > for that reason for private/mirror faults.
> Hmm, TDX does set PFERR_WRITE_MASK in the error_code when fault->prefetch is
> false (since exit_qual is set to EPT_VIOLATION_ACC_WRITE in
> tdx_handle_ept_violation()).
> 
> PFERR_PRESENT_MASK is always unset.
> 
> page_fault_can_be_fast() does always return false for private mirror faults
> though, due to the reason in
> https://lore.kernel.org/kvm/aEp6pDQgbjsfrg2h@yzhao56-desk.sh.intel.com :)

Seems cleanup worthy to me, but not a bug. I think we should follow up,
depending on the scope of Sean's cleanup.