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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] KVM: x86/mmu: Avoid retpoline on ->page_fault() with TDP
Date: Fri, 07 Feb 2020 10:29:16 +0100	[thread overview]
Message-ID: <878sleg2z7.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20200206221434.23790-1-sean.j.christopherson@intel.com>

Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Wrap calls to ->page_fault() with a small shim to directly invoke the
> TDP fault handler when the kernel is using retpolines and TDP is being
> used.  Denote the TDP fault handler by nullifying mmu->page_fault, and
> annotate the TDP path as likely to coerce the compiler into preferring
> the TDP path.
>
> Rename tdp_page_fault() to kvm_tdp_page_fault() as it's exposed outside
> of mmu.c to allow inlining the shim.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---

Out of pure curiosity, if we do something like

if (vcpu->arch.mmu->page_fault == tdp_page_fault)
    tdp_page_fault(...)
else if (vcpu->arch.mmu->page_fault == nonpaging_page_fault)
   nonpaging_page_fault(...)
...

we also defeat the retpoline, right? Should we use this technique
... everywhere? :-)

-- 
Vitaly


  reply	other threads:[~2020-02-07  9:29 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-06 22:14 Sean Christopherson
2020-02-07  9:29 ` Vitaly Kuznetsov [this message]
2020-02-07 15:55   ` Sean Christopherson
2020-02-07 16:15     ` Vitaly Kuznetsov
2020-02-12 11:55     ` Paolo Bonzini
2020-02-12 16:22       ` Sean Christopherson

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