Re: [PATCH] kvm/x86: simplify kvm_mmu_do_page_fault() a little bit

["Jürgen Groß" <jgross@suse.com>]

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On 22.10.24 19:01, Sean Christopherson wrote:
> On Tue, Oct 22, 2024, Juergen Gross wrote:
>> Testing whether to call kvm_tdp_page_fault() or
>> vcpu->arch.mmu->page_fault() doesn't make sense, as kvm_tdp_page_fault()
>> is selected only if vcpu->arch.mmu->page_fault == kvm_tdp_page_fault.
> 
> It does when retpolines are enabled and significantly inflate the cost of the
> indirect call.  This is a hot path in various scenarios, but KVM can't use
> static_call() to avoid the retpoline due to mmu->page_fault being a property of
> the current vCPU.  Only kvm_tdp_page_fault() is special cased because all other
> mmu->page_fault targets are slow-ish and/or we don't care terribly about their
> performance.

Fair enough. :-)

I'll modify the patch to add a comment in this regard in order to avoid
similar simplification attempts in the future.


Juergen

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