linux-kernel - [RFC v2 4/7] KVM: MMU: Refactor pkr

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Date:   Wed, 14 Oct 2020 10:11:53 +0800
From:   Chenyi Qiang <chenyi.qiang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC v2 4/7] KVM: MMU: Refactor pkr_mask to cache condition

pkr_mask bitmap indicates if protection key checks are needed for user
pages currently. It is indexed by page fault error code bits [4:1] with
PFEC.RSVD replaced by the ACC_USER_MASK from the page tables. Refactor
it by reverting to the use of PFEC.RSVD. After that, PKS and PKU can
share the same bitmap.

Signed-off-by: Chenyi Qiang <chenyi.qiang@...el.com>
---
 arch/x86/kvm/mmu.h     | 10 ++++++----
 arch/x86/kvm/mmu/mmu.c | 16 ++++++++++------
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 306608248594..597b9159c10b 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -204,11 +204,13 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 		* index of the protection domain, so pte_pkey * 2 is
 		* is the index of the first bit for the domain.
 		*/
-		pkr_bits = (vcpu->arch.pkru >> (pte_pkey * 2)) & 3;
+		if (pte_access & PT_USER_MASK)
+			pkr_bits = (vcpu->arch.pkru >> (pte_pkey * 2)) & 3;
+		else
+			pkr_bits = 0;
 
-		/* clear present bit, replace PFEC.RSVD with ACC_USER_MASK. */
-		offset = (pfec & ~1) +
-			((pte_access & PT_USER_MASK) << (PFERR_RSVD_BIT - PT_USER_SHIFT));
+		/* clear present bit */
+		offset = (pfec & ~1);
 
 		pkr_bits &= mmu->pkr_mask >> offset;
 		errcode |= -pkr_bits & PFERR_PK_MASK;
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 834a95cf49fa..f9814ab0596d 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4716,21 +4716,25 @@ static void update_pkr_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 
 	for (bit = 0; bit < ARRAY_SIZE(mmu->permissions); ++bit) {
 		unsigned pfec, pkey_bits;
-		bool check_pkey, check_write, ff, uf, wf, pte_user;
+		bool check_pkey, check_write, ff, uf, wf, rsvdf;
 
 		pfec = bit << 1;
 		ff = pfec & PFERR_FETCH_MASK;
 		uf = pfec & PFERR_USER_MASK;
 		wf = pfec & PFERR_WRITE_MASK;
 
-		/* PFEC.RSVD is replaced by ACC_USER_MASK. */
-		pte_user = pfec & PFERR_RSVD_MASK;
+		/*
+		 * PFERR_RSVD_MASK bit is not set if the
+		 * access is subject to PK restrictions.
+		 */
+		rsvdf = pfec & PFERR_RSVD_MASK;
 
 		/*
-		 * Only need to check the access which is not an
-		 * instruction fetch and is to a user page.
+		 * need to check the access which is not an
+		 * instruction fetch and is not a rsvd fault.
 		 */
-		check_pkey = (!ff && pte_user);
+		check_pkey = (!ff && !rsvdf);
+
 		/*
 		 * write access is controlled by PKRU if it is a
 		 * user access or CR0.WP = 1.
-- 
2.17.1