linux-kernel - [RFC PATCH 2/2] KVM: MMU: return page fault error code from permission

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Message-Id: <1457437538-65867-3-git-send-email-pbonzini@redhat.com>
Date:	Tue,  8 Mar 2016 12:45:38 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:	guangrong.xiao@...ux.intel.com, huaitong.han@...el.com
Subject: [RFC PATCH 2/2] KVM: MMU: return page fault error code from permission_fault

Intel's new PKU extension introduces a bit of the page fault error code
that must be dynamically computed after the PTE lookup (unlike I/D, U/S
and W/R).  To ease this, these two patches make permission_fault return
the page fault error code.

Right now it only adds the P bit to the input parameter "pfec", but PKU
can change that.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/mmu.h         | 15 ++++++++++-----
 arch/x86/kvm/paging_tmpl.h |  5 ++---
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 58fe98a0a526..8b2b3dfca1ae 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -141,11 +141,15 @@ static inline bool is_write_protection(struct kvm_vcpu *vcpu)
 }
 
 /*
- * Will a fault with a given page-fault error code (pfec) cause a permission
- * fault with the given access (in ACC_* format)?
+ * Check if a given access (described through the I/D, W/R and U/S bits of a
+ * page fault error code pfec) causes a permission fault with the given PTE
+ * access rights (in ACC_* format).
+ *
+ * Return zero if the access does not fault; return the page fault error code
+ * if the access faults.
  */
-static inline bool permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
-				    unsigned pte_access, unsigned pfec)
+static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
+				  unsigned pte_access, unsigned pfec)
 {
 	int cpl = kvm_x86_ops->get_cpl(vcpu);
 	unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
@@ -169,7 +173,8 @@ static inline bool permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 
 	WARN_ON(pfec & PFERR_RSVD_MASK);
 
-	return (mmu->permissions[index] >> pte_access) & 1;
+	pfec |= PFERR_PRESENT_MASK;
+	return -((mmu->permissions[index] >> pte_access) & 1) & pfec;
 }
 
 void kvm_mmu_invalidate_zap_all_pages(struct kvm *kvm);
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 285858d3223b..4a6866dab848 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -370,10 +370,9 @@ retry_walk:
 		walker->ptes[walker->level - 1] = pte;
 	} while (!is_last_gpte(mmu, walker->level, pte));
 
-	if (unlikely(permission_fault(vcpu, mmu, pte_access, access))) {
-		errcode |= PFERR_PRESENT_MASK;
+	errcode = permission_fault(vcpu, mmu, pte_access, errcode);
+	if (unlikely(errcode))
 		goto error;
-	}
 
 	gfn = gpte_to_gfn_lvl(pte, walker->level);
 	gfn += (addr & PT_LVL_OFFSET_MASK(walker->level)) >> PAGE_SHIFT;
-- 
1.8.3.1