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: Sean Christopherson <sean.j.christopherson@intel.com>,
	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: [PATCH] KVM: x86/mmu: Avoid retpoline on ->page_fault() with TDP
Date: Thu,  6 Feb 2020 14:14:34 -0800	[thread overview]
Message-ID: <20200206221434.23790-1-sean.j.christopherson@intel.com> (raw)

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>
---

Haven't done any performance testing, this popped into my head when mucking
with the 5-level page table crud as an easy way to shave cycles in the
happy path.

 arch/x86/kvm/mmu.h     | 13 +++++++++++++
 arch/x86/kvm/mmu/mmu.c | 16 ++++++++++------
 arch/x86/kvm/x86.c     |  2 +-
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index d55674f44a18..9277ee8a54a5 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -102,6 +102,19 @@ static inline void kvm_mmu_load_cr3(struct kvm_vcpu *vcpu)
 					      kvm_get_active_pcid(vcpu));
 }
 
+int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
+		       bool prefault);
+
+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))
+		return kvm_tdp_page_fault(vcpu, cr2_or_gpa, err, prefault);
+#endif
+	return vcpu->arch.mmu->page_fault(vcpu, cr2_or_gpa, err, prefault);
+}
+
 /*
  * Currently, we have two sorts of write-protection, a) the first one
  * write-protects guest page to sync the guest modification, b) another one is
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 7011a4e54866..5267f1440677 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4219,8 +4219,8 @@ int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code,
 }
 EXPORT_SYMBOL_GPL(kvm_handle_page_fault);
 
-static int tdp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
-			  bool prefault)
+int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
+		       bool prefault)
 {
 	int max_level;
 
@@ -4925,7 +4925,12 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
 		return;
 
 	context->mmu_role.as_u64 = new_role.as_u64;
-	context->page_fault = tdp_page_fault;
+#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;
@@ -5436,9 +5441,8 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
 	}
 
 	if (r == RET_PF_INVALID) {
-		r = vcpu->arch.mmu->page_fault(vcpu, cr2_or_gpa,
-					       lower_32_bits(error_code),
-					       false);
+		r = kvm_mmu_do_page_fault(vcpu, cr2_or_gpa,
+					  lower_32_bits(error_code), false);
 		WARN_ON(r == RET_PF_INVALID);
 	}
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fbabb2f06273..39251ecafd2b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10182,7 +10182,7 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
 	      work->arch.cr3 != vcpu->arch.mmu->get_cr3(vcpu))
 		return;
 
-	vcpu->arch.mmu->page_fault(vcpu, work->cr2_or_gpa, 0, true);
+	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true);
 }
 
 static inline u32 kvm_async_pf_hash_fn(gfn_t gfn)
-- 
2.24.1


             reply	other threads:[~2020-02-06 22:14 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-06 22:14 Sean Christopherson [this message]
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

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=20200206221434.23790-1-sean.j.christopherson@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).