linux-kernel - [RFC PATCH 05/10] x86/pkeys: Drop the preempt-disable section

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Message-Id: <20180912133353.20595-6-bigeasy@linutronix.de>
Date:   Wed, 12 Sep 2018 15:33:48 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [RFC PATCH 05/10] x86/pkeys: Drop the preempt-disable section

From: Rik van Riel <riel@...riel.com>

The fpu->initialized flag should not be changed underneath us. This might be a
fallout during the removal of the LazyFPU support. The FPU is marked
initialized as soon as the state has been set to an initial value. It does not
signal if the CPU's FPU registers are loaded.

Signed-off-by: Rik van Riel <riel@...riel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 arch/x86/mm/pkeys.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c
index c7a7b6bd64009..6e91529fe2a30 100644
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -53,17 +53,13 @@ int __execute_only_pkey(struct mm_struct *mm)
 	 * dance to set PKRU if we do not need to.  Check it
 	 * first and assume that if the execute-only pkey is
 	 * write-disabled that we do not have to set it
-	 * ourselves.  We need preempt off so that nobody
-	 * can make fpregs inactive.
+	 * ourselves.
 	 */
-	preempt_disable();
 	if (!need_to_set_mm_pkey &&
 	    current->thread.fpu.initialized &&
 	    !__pkru_allows_read(read_pkru(), execute_only_pkey)) {
-		preempt_enable();
 		return execute_only_pkey;
 	}
-	preempt_enable();
 
 	/*
 	 * Set up PKRU so that it denies access for everything
-- 
2.19.0