Re: [PATCH 2/7] KVM: x86/mmu: Return RET_PF* instead of 1 in kvm_mmu_page_fault()

[Yan Zhao]

On Wed, Jan 15, 2025 at 06:24:43AM +0800, Edgecombe, Rick P wrote:
> On Mon, 2025-01-13 at 10:11 +0800, Yan Zhao wrote:
> > Return RET_PF* (excluding RET_PF_EMULATE/RET_PF_CONTINUE/RET_PF_INVALID)
> > instead of 1 in kvm_mmu_page_fault().
> > 
> > The callers of kvm_mmu_page_fault() are KVM page fault handlers (i.e.,
> > npf_interception(), handle_ept_misconfig(), __vmx_handle_ept_violation(),
> > kvm_handle_page_fault()). They either check if the return value is > 0 (as
> > in npf_interception()) or pass it further to vcpu_run() to decide whether
> > to break out of the kernel loop and return to the user when r <= 0.
> > Therefore, returning any positive value is equivalent to returning 1.
> > 
> > Warn if r == RET_PF_CONTINUE (which should not be a valid value) to ensure
> > a positive return value.
> > 
> > This is a preparation to allow TDX's EPT violation handler to check the
> > RET_PF* value and retry internally for RET_PF_RETRY.
> > 
> > No functional changes are intended.
> 
> Any reason why this can't go ahead of the TDX patches? Seems pretty generic
> cleanup.
Hmm, I wouldn't consider this a cleanup, as returning 1 to indicate continuation
of the kernel loop is a well-established convention in arch/x86/kvm.

Returning a positive RET_PF_* in this patch is primarily a preparatory step for
the subsequent patch,
"KVM: TDX: Retry locally in TDX EPT violation handler on RET_PF_RETRY".