linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: x86/mmu: Avoid retpoline on ->page_fault() with TDP
Date: Wed, 12 Feb 2020 08:22:20 -0800	[thread overview]
Message-ID: <20200212162220.GA15617@linux.intel.com> (raw)
In-Reply-To: <408bfd4c-7407-48cd-95fb-db44a7c1c2bf@redhat.com>

On Wed, Feb 12, 2020 at 12:55:09PM +0100, Paolo Bonzini wrote:
> On 07/02/20 16:55, Sean Christopherson wrote:
> > It becomes a matter of weighing the maintenance cost and robustness against
> > the performance benefits.  For the TDP case, amost no one (that cares about
> > performance) uses shadow paging, the change is very explicit, tiny and
> > isolated, and TDP page fault are a hot path, e.g. when booting the VM.
> > I.e. low maintenance overhead, still robust, and IMO worth the shenanigans.
> 
> The "NULL" trick does not seem needed though.  Any objections to this?

Nope, no objections.

> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 9277ee8a54a5..a647601c9e1c 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -109,7 +109,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>  					u32 err, bool prefault)
>  {
>  #ifdef CONFIG_RETPOLINE
> -	if (likely(!vcpu->arch.mmu->page_fault))
> +	if (likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault))
>  		return kvm_tdp_page_fault(vcpu, cr2_or_gpa, err, prefault);
>  #endif
>  	return vcpu->arch.mmu->page_fault(vcpu, cr2_or_gpa, err, prefault);
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 5267f1440677..87e9ba27ada1 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4925,12 +4925,7 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
>  		return;
>  
>  	context->mmu_role.as_u64 = new_role.as_u64;
> -#ifdef CONFIG_RETPOLINE
> -	/* Nullify ->page_fault() to use direct kvm_tdp_page_fault() call. */
> -	context->page_fault = NULL;
> -#else
>  	context->page_fault = kvm_tdp_page_fault;
> -#endif
>  	context->sync_page = nonpaging_sync_page;
>  	context->invlpg = nonpaging_invlpg;
>  	context->update_pte = nonpaging_update_pte;
> 
> Paolo
> 

      reply	other threads:[~2020-02-12 16:22 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
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 [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200212162220.GA15617@linux.intel.com \
    --to=sean.j.christopherson@intel.com \
    --cc=jmattson@google.com \
    --cc=joro@8bytes.org \
    --cc=kvm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=pbonzini@redhat.com \
    --cc=vkuznets@redhat.com \
    --cc=wanpengli@tencent.com \
    --subject='Re: [PATCH] KVM: x86/mmu: Avoid retpoline on ->page_fault() with TDP' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).