Re: [PATCH] x86/xsave: Robustify and merge macros
From: Quentin Casasnovas
Date: Thu Apr 02 2015 - 11:50:32 EST
On Thu, Apr 02, 2015 at 03:11:22PM +0200, Borislav Petkov wrote:
> From: Borislav Petkov <bp@xxxxxxx>
> Previously, we did call an XSAVE/XRSTOR variant through alternatives
> and did potential exception handling resulting from the instruction
> execution in a second inline asm. Which was misleading and error prone,
> 06c8173eb92b ("x86/fpu/xsaves: Fix improper uses of __ex_table")
> for an example.
> Add single macros which combine the alternatives and the exception
FWIW I think this looks much nicer! I have a couple of comments though,
apologies in advance if they aren't relevant :)
> While at it, remove the SYSTEM_BOOTING checks in favor of
> static_cpu_has_safe() which works regardless of system state.
I thought the SYSTEM_BOOTING checks were present to make sure we call these
functions only when the alternative instructions had *not* been applied
(i.e. when SYSTEM_BOOTING). We could have added the opposite checks in
xsave_state()/xrstor_state() to make sure the alternative instructions are
applied when these are called (i.e. when !SYSTEM_BOOTING).
In the unlikely event where I'm not wrong about this, having a nicely named
helper altinstr_are_applied() instead of manually checking the system_state
variable would probably help!
But maybe we're pretty confident this will not happen anyway?
> Cleanup comments.
> Signed-off-by: Borislav Petkov <bp@xxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> arch/x86/include/asm/xsave.h | 141 ++++++++++++++++++++++---------------------
> 1 file changed, 73 insertions(+), 68 deletions(-)
> diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h
> index c9a6d68b8d62..e6c7986c95df 100644
> --- a/arch/x86/include/asm/xsave.h
> +++ b/arch/x86/include/asm/xsave.h
> @@ -67,6 +67,66 @@ extern int init_fpu(struct task_struct *child);
> _ASM_EXTABLE(1b, 3b) \
> : [err] "=r" (err)
> +#define XSTATE_OP(op, st, lmask, hmask, err) \
> + asm volatile("1:" op "\n\t" \
> + "2:\n\t" \
> + "xor %[err], %[err]\n" \
Are you not invariably clearing err here? If the instruction fault, we go
to label '3' which does 'err = -1; goto 2', which clears err. Same remark
Probably missing something..
Also, tiny consistency nit, maybe use "\n\t" everywhere?
> + ".pushsection .fixup,\"ax\"\n\t" \
> + "3: movl $-1,%[err]\n\t" \
> + "jmp 2b\n\t" \
> + ".popsection\n\t" \
> + _ASM_EXTABLE(1b, 3b) \
> + : [err] "=r" (err) \
> + : "D" (st), "m" (*st), "a" (lmask), "d" (hmask) \
> + : "memory")
I've tried compiling this on top of v4.0-rc5 and I get a compile error
because alt_end_marker isn't defined. Which other patches should I take to
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