Save eflags during task switch but only restore them if the next
task has different values that affect system operation.
Original idea by Zach Amsden.
Signed-off-by: Chuck Ebbert <[email protected]>
---
arch/i386/kernel/ioport.c | 8 ++++----
arch/i386/kernel/process.c | 6 +++---
include/asm-i386/processor.h | 30 ++++++++++++++++++++----------
include/asm-i386/system.h | 12 +++++++-----
4 files changed, 34 insertions(+), 22 deletions(-)
--- 2.6.19-rc4-32smp.orig/include/asm-i386/processor.h
+++ 2.6.19-rc4-32smp/include/asm-i386/processor.h
@@ -143,6 +143,12 @@ static inline void detect_ht(struct cpui
#define X86_EFLAGS_VIP 0x00100000 /* Virtual Interrupt Pending */
#define X86_EFLAGS_ID 0x00200000 /* CPUID detection flag */
+/*
+ * EFLAGS bits that affect system operation
+ */
+#define X86_EFLAGS_SYSTEM ~(X86_EFLAGS_OF | X86_EFLAGS_SF | X86_EFLAGS_ZF | \
+ X86_EFLAGS_AF | X86_EFLAGS_PF | X86_EFLAGS_ZF)
+
static inline void __cpuid(unsigned int *eax, unsigned int *ebx,
unsigned int *ecx, unsigned int *edx)
{
@@ -449,6 +455,7 @@ struct thread_struct {
unsigned long sysenter_cs;
unsigned long eip;
unsigned long esp;
+ unsigned long eflags;
unsigned long fs;
unsigned long gs;
/* Hardware debugging registers */
@@ -464,7 +471,6 @@ struct thread_struct {
unsigned int saved_fs, saved_gs;
/* IO permissions */
unsigned long *io_bitmap_ptr;
- unsigned long iopl;
/* max allowed port in the bitmap, in bytes: */
unsigned long io_bitmap_max;
};
@@ -521,20 +527,24 @@ static inline void load_esp0(struct tss_
: /* no output */ \
:"r" (value))
+static inline unsigned get_eflags(void) {
+ unsigned eflags;
+
+ asm volatile ("pushfl ; popl %0" : "=g" (eflags));
+
+ return eflags;
+}
+
+static inline void set_eflags(unsigned eflags) {
+ asm volatile ("pushl %0 ; popfl" : : "g" (eflags));
+}
+
/*
* Set IOPL bits in EFLAGS from given mask
*/
static inline void set_iopl_mask(unsigned mask)
{
- 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));
+ set_eflags((get_eflags() & ~X86_EFLAGS_IOPL) | (mask & X86_EFLAGS_IOPL));
}
/* Forward declaration, a strange C thing */
--- 2.6.19-rc4-32smp.orig/arch/i386/kernel/process.c
+++ 2.6.19-rc4-32smp/arch/i386/kernel/process.c
@@ -681,10 +681,10 @@ struct task_struct fastcall * __switch_t
loadsegment(gs, next->gs);
/*
- * Restore IOPL if needed.
+ * Restore eflags if system flags are different in next task.
*/
- if (unlikely(prev->iopl != next->iopl))
- set_iopl_mask(next->iopl);
+ if (unlikely((get_eflags() ^ next->eflags) & X86_EFLAGS_SYSTEM))
+ set_eflags(next->eflags);
/*
* Now maybe handle debug registers and/or IO bitmaps
--- 2.6.19-rc4-32smp.orig/include/asm-i386/system.h
+++ 2.6.19-rc4-32smp/include/asm-i386/system.h
@@ -14,23 +14,25 @@ extern struct task_struct * FASTCALL(__s
/*
* Saving eflags is important. It switches not only IOPL between tasks,
* it also protects other tasks from NT leaking through sysenter etc.
+ * (eflags will be restored in __switch_to() only if necessary.)
*/
#define switch_to(prev,next,last) do { \
unsigned long esi,edi; \
asm volatile("pushfl\n\t" /* Save flags */ \
+ "popl %2\n\t" \
"pushl %%ebp\n\t" \
"movl %%esp,%0\n\t" /* save ESP */ \
- "movl %5,%%esp\n\t" /* restore ESP */ \
+ "movl %6,%%esp\n\t" /* restore ESP */ \
"movl $1f,%1\n\t" /* save EIP */ \
- "pushl %6\n\t" /* restore EIP */ \
+ "pushl %7\n\t" /* restore EIP */ \
"jmp __switch_to\n" \
"1:\t" \
- "popl %%ebp\n\t" \
- "popfl" \
+ "popl %%ebp" \
:"=m" (prev->thread.esp),"=m" (prev->thread.eip), \
+ "=m" (prev->thread.eflags), \
"=a" (last),"=S" (esi),"=D" (edi) \
:"m" (next->thread.esp),"m" (next->thread.eip), \
- "2" (prev), "d" (next)); \
+ "3" (prev), "d" (next)); \
} while (0)
#define _set_base(addr,base) do { unsigned long __pr; \
--- 2.6.19-rc4-32smp.orig/arch/i386/kernel/ioport.c
+++ 2.6.19-rc4-32smp/arch/i386/kernel/ioport.c
@@ -137,7 +137,7 @@ asmlinkage long sys_iopl(unsigned long u
volatile struct pt_regs * regs = (struct pt_regs *) &unused;
unsigned int level = regs->ebx;
unsigned int old = (regs->eflags >> 12) & 3;
- struct thread_struct *t = ¤t->thread;
+ unsigned int iopl;
if (level > 3)
return -EINVAL;
@@ -146,8 +146,8 @@ asmlinkage long sys_iopl(unsigned long u
if (!capable(CAP_SYS_RAWIO))
return -EPERM;
}
- t->iopl = level << 12;
- regs->eflags = (regs->eflags & ~X86_EFLAGS_IOPL) | t->iopl;
- set_iopl_mask(t->iopl);
+ iopl = level << 12;
+ regs->eflags = (regs->eflags & ~X86_EFLAGS_IOPL) | iopl;
+ set_iopl_mask(iopl);
return 0;
}
--
Chuck