linux-kernel - [PATCH 1/3] x86: Remove native_set_iopl

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Date:   Wed, 14 Jun 2017 08:40:30 -0400
From:   Brian Gerst <brgerst@...il.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>, "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: [PATCH 1/3] x86: Remove native_set_iopl_mask()

On native hardware, IRET and POPF will correctly restore the IOPL bits.
This was left over from when the SYSEXIT path did not restore the user
flags with POPF.

Signed-off-by: Brian Gerst <brgerst@...il.com>
---
 arch/x86/include/asm/processor.h | 21 +--------------------
 arch/x86/kernel/paravirt.c       |  2 +-
 2 files changed, 2 insertions(+), 21 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 3cada99..06c4795 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -482,25 +482,6 @@ struct thread_struct {
  */
 #define TS_COMPAT		0x0002	/* 32bit syscall active (64BIT)*/
 
-/*
- * Set IOPL bits in EFLAGS from given mask
- */
-static inline void native_set_iopl_mask(unsigned mask)
-{
-#ifdef CONFIG_X86_32
-	unsigned int reg;
-
-	asm volatile ("pushfl;"
-		      "popl %0;"
-		      "andl %1, %0;"
-		      "orl %2, %0;"
-		      "pushl %0;"
-		      "popfl"
-		      : "=&r" (reg)
-		      : "i" (~X86_EFLAGS_IOPL), "r" (mask));
-#endif
-}
-
 static inline void
 native_load_sp0(struct tss_struct *tss, struct thread_struct *thread)
 {
@@ -542,7 +523,7 @@ static inline void load_sp0(struct tss_struct *tss,
 	native_load_sp0(tss, thread);
 }
 
-#define set_iopl_mask native_set_iopl_mask
+static inline void set_iopl_mask(unsigned mask) { }
 #endif /* CONFIG_PARAVIRT */
 
 /* Free all resources held by a thread. */
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 3586996..1d50eb5 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -367,7 +367,7 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
 	.iret = native_iret,
 	.swapgs = native_swapgs,
 
-	.set_iopl_mask = native_set_iopl_mask,
+	.set_iopl_mask = paravirt_nop,
 	.io_delay = native_io_delay,
 
 	.start_context_switch = paravirt_nop,
-- 
2.9.4