linux-kernel - Re: [PATCH 3/7] KVM: x86/mmu: Extract __kvm_mmu_do_page

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Date: Wed, 17 Apr 2024 12:47:34 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	isaku.yamahata@...el.com, xiaoyao.li@...el.com,
	binbin.wu@...ux.intel.com, seanjc@...gle.com,
	rick.p.edgecombe@...el.com, isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH 3/7] KVM: x86/mmu: Extract __kvm_mmu_do_page_fault()

On Wed, Apr 17, 2024 at 11:34:46AM -0400,
Paolo Bonzini <pbonzini@...hat.com> wrote:

> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Extract out __kvm_mmu_do_page_fault() from kvm_mmu_do_page_fault().  The
> inner function is to initialize struct kvm_page_fault and to call the fault
> handler, and the outer function handles updating stats and converting
> return code.  KVM_MAP_MEMORY will call the KVM page fault handler.

To clarify to no update vcpu.stat, let me update the last sentence.

  KVM_MAP_MEMORY will call the KVM page fault handler without vcpu stat that
  doesn't make sense for pre-population because pre-population (outside TDX) has
  the purpose of avoiding page faults

> This patch makes the emulation_type always set irrelevant to the return
> code.  kvm_mmu_page_fault() is the only caller of kvm_mmu_do_page_fault(),
> and references the value only when PF_RET_EMULATE is returned.  Therefore,
> this adjustment doesn't affect functionality.

For the technical correctness, let me mention about NULL emulation_type.
I added "," and "with non-NULL emulation_type" to the second sentence.
  https://lore.kernel.org/all/621c260399a05338ba6d034e275e19714ad3665c.camel@intel.com/

  This patch makes the emulation_type always set, irrelevant to the return
  code. kvm_mmu_page_fault() is the only caller of kvm_mmu_do_page_fault() with
  non-NULL emulation_type and references the value only when PF_RET_EMULATE is
  returned. Therefore, this adjustment doesn't affect functionality.

-- 
Isaku Yamahata <isaku.yamahata@...el.com>