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[PATCH 1/7] x86/vm86: Clean up saved_fs/gs

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  [PATCH 1/7] x86/vm86: Clean up saved_fs/gs Brian Gerst <brgerst@gmail.com> - 2015-07-16 13:50 +0200
    Re: [PATCH 1/7] x86/vm86: Clean up saved_fs/gs Andy Lutomirski <luto@amacapital.net> - 2015-07-16 17:50 +0200
      Re: [PATCH 1/7] x86/vm86: Clean up saved_fs/gs Brian Gerst <brgerst@gmail.com> - 2015-07-16 18:00 +0200

#1185782 — [PATCH 1/7] x86/vm86: Clean up saved_fs/gs

There is no need to save FS and non-lazy GS outside the 32-bit regs.  Lazy GS
still needs to be saved because it wasn't saved on syscall entry.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
---
 arch/x86/include/asm/processor.h | 3 ++-
 arch/x86/kernel/vm86_32.c        | 6 ++----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 43e6519..a4b5c6a 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -410,9 +410,10 @@ struct thread_struct {
 	unsigned long		v86flags;
 	unsigned long		v86mask;
 	unsigned long		saved_sp0;
-	unsigned int		saved_fs;
+#ifdef CONFIG_X86_32_LAZY_GS
 	unsigned int		saved_gs;
 #endif
+#endif
 	/* IO permissions: */
 	unsigned long		*io_bitmap_ptr;
 	unsigned long		iopl;
diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
index fc9db6e..75eab83 100644
--- a/arch/x86/kernel/vm86_32.c
+++ b/arch/x86/kernel/vm86_32.c
@@ -159,8 +159,7 @@ struct pt_regs *save_v86_state(struct kernel_vm86_regs *regs)
 
 	ret = KVM86->regs32;
 
-	ret->fs = current->thread.saved_fs;
-	set_user_gs(ret, current->thread.saved_gs);
+	lazy_load_gs(current->thread.saved_gs);
 
 	return ret;
 }
@@ -315,8 +314,7 @@ static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk
  */
 	info->regs32->ax = VM86_SIGNAL;
 	tsk->thread.saved_sp0 = tsk->thread.sp0;
-	tsk->thread.saved_fs = info->regs32->fs;
-	tsk->thread.saved_gs = get_user_gs(info->regs32);
+	lazy_save_gs(tsk->thread.saved_gs);
 
 	tss = &per_cpu(cpu_tss, get_cpu());
 	tsk->thread.sp0 = (unsigned long) &info->VM86_TSS_ESP0;
-- 
2.4.3

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#1186006

On Thu, Jul 16, 2015 at 4:46 AM, Brian Gerst <brgerst@gmail.com> wrote:
> There is no need to save FS and non-lazy GS outside the 32-bit regs.  Lazy GS
> still needs to be saved because it wasn't saved on syscall entry.

I think I'm missing something.  Why can't you just lazy_save_gs into regs32->gs?

--Andy
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#1186025

On Thu, Jul 16, 2015 at 11:45 AM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Thu, Jul 16, 2015 at 4:46 AM, Brian Gerst <brgerst@gmail.com> wrote:
>> There is no need to save FS and non-lazy GS outside the 32-bit regs.  Lazy GS
>> still needs to be saved because it wasn't saved on syscall entry.
>
> I think I'm missing something.  Why can't you just lazy_save_gs into regs32->gs?
>
> --Andy

That is probably a better idea.  The gs field exists in pt_regs but is
unused in lazy mode.  Could also change switch_to() to store GS in
pt_regs instead of thread.gs, which would simplify ptrace a bit.

--
Brian Gerst
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