linux-kernel - [tip: x86/fpu] x86/pkru: Remove xstate fiddling from write

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Message-ID: <162448613653.395.16973019914888523169.tip-bot2@tip-bot2>
Date:   Wed, 23 Jun 2021 22:08:56 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...e.de>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/fpu] x86/pkru: Remove xstate fiddling from write_pkru()

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     72a6c08c44e4460e39315ca828f60b8d5afd6b19
Gitweb:        https://git.kernel.org/tip/72a6c08c44e4460e39315ca828f60b8d5afd6b19
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Wed, 23 Jun 2021 14:02:23 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Wed, 23 Jun 2021 19:55:51 +02:00

x86/pkru: Remove xstate fiddling from write_pkru()

The PKRU value of a task is stored in task->thread.pkru when the task is
scheduled out. PKRU is restored on schedule in from there. So keeping the
XSAVE buffer up to date is a pointless exercise.

Remove the xstate fiddling and cleanup all related functions.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Borislav Petkov <bp@...e.de>
Link: https://lkml.kernel.org/r/20210623121456.897372712@linutronix.de
---
 arch/x86/include/asm/pkru.h          | 17 ++++-------------
 arch/x86/include/asm/special_insns.h | 14 +-------------
 arch/x86/kvm/x86.c                   |  4 ++--
 3 files changed, 7 insertions(+), 28 deletions(-)

diff --git a/arch/x86/include/asm/pkru.h b/arch/x86/include/asm/pkru.h
index 7e45509..ccc539f 100644
--- a/arch/x86/include/asm/pkru.h
+++ b/arch/x86/include/asm/pkru.h
@@ -41,23 +41,14 @@ static inline u32 read_pkru(void)
 
 static inline void write_pkru(u32 pkru)
 {
-	struct pkru_state *pk;
-
 	if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
 		return;
-
-	pk = get_xsave_addr(&current->thread.fpu.state.xsave, XFEATURE_PKRU);
-
 	/*
-	 * The PKRU value in xstate needs to be in sync with the value that is
-	 * written to the CPU. The FPU restore on return to userland would
-	 * otherwise load the previous value again.
+	 * WRPKRU is relatively expensive compared to RDPKRU.
+	 * Avoid WRPKRU when it would not change the value.
 	 */
-	fpregs_lock();
-	if (pk)
-		pk->pkru = pkru;
-	__write_pkru(pkru);
-	fpregs_unlock();
+	if (pkru != rdpkru())
+		wrpkru(pkru);
 }
 
 static inline void pkru_write_default(void)
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 2acd6cb..f3fbb84 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -104,25 +104,13 @@ static inline void wrpkru(u32 pkru)
 		     : : "a" (pkru), "c"(ecx), "d"(edx));
 }
 
-static inline void __write_pkru(u32 pkru)
-{
-	/*
-	 * WRPKRU is relatively expensive compared to RDPKRU.
-	 * Avoid WRPKRU when it would not change the value.
-	 */
-	if (pkru == rdpkru())
-		return;
-
-	wrpkru(pkru);
-}
-
 #else
 static inline u32 rdpkru(void)
 {
 	return 0;
 }
 
-static inline void __write_pkru(u32 pkru)
+static inline void wrpkru(u32 pkru)
 {
 }
 #endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 07f7888..8ee7add 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -943,7 +943,7 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
 	    (kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
 	     (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU)) &&
 	    vcpu->arch.pkru != vcpu->arch.host_pkru)
-		__write_pkru(vcpu->arch.pkru);
+		write_pkru(vcpu->arch.pkru);
 }
 EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);
 
@@ -957,7 +957,7 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
 	     (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU))) {
 		vcpu->arch.pkru = rdpkru();
 		if (vcpu->arch.pkru != vcpu->arch.host_pkru)
-			__write_pkru(vcpu->arch.host_pkru);
+			write_pkru(vcpu->arch.host_pkru);
 	}
 
 	if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE)) {