Re: [PATCH RFC 0/2] x86/fpu: avoid "xstate_fault" in xsave_user/xrestore_user

Borislav Petkov
2015-03-16T14:37:43Z

On Sun, Mar 15, 2015 at 05:49:48PM +0100, Oleg Nesterov wrote:
> Hello.
>
> Another a bit off-topic change, but I'd like to finish the discussion
> with Quentin.
>
> And almost cosmetic. But I added the RFC tag to make it clear that this
> needs a review from someone who understands gcc-asm better. In particular
> I am worried if that dummy "=m" (*buf) is actually correct.
>
>
> And I agree with Quentin, user_insn/check_insn can be improved to allow
> clobbers, more flexible "output", etc. But imo they already can make this
> code look a bit better, and "xstate_fault" must die eventually.

FWIW, I did poke at that but there's still something wrong with my macros, will
take a look when I get a chance:

---
arch/x86/include/asm/xsave.h | 130 +++++++++++++++++++++++++++----------------
1 file changed, 82 insertions(+), 48 deletions(-)

diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h
index c9a6d68b8d62..a35e9d49843d 100644
--- a/arch/x86/include/asm/xsave.h
+++ b/arch/x86/include/asm/xsave.h
@@ -67,6 +67,51 @@ 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" \
+ ".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")
+
+/*
+ * 661 and alt_end_marker labels below are defined in ALTERNATIVE*
+ * and we're reusing them here so as not to clutter this macro
+ * unnecessarily.
+ */
+#define XSTATE_XSAVE(st, lmask, hmask, err) \
+ asm volatile(ALTERNATIVE_2(XSAVE, \
+ XSAVEOPT, X86_FEATURE_XSAVEOPT, \
+ XSAVES, X86_FEATURE_XSAVES) \
+ "\n" \
+ ".pushsection .fixup,\"ax\"\n" \
+ "3: movl $-1, %[err]\n" \
+ "jmp " alt_end_marker "b\n" \
+ ".popsection\n" \
+ _ASM_EXTABLE(661b, 3b) \
+ : [err] "=r" (err) \
+ : "D" (st), "a" (lmask), "d" (hmask) \
+ : "memory")
+
+#define XSTATE_XRESTORE(st, lmask, hmask, err) \
+ asm volatile(ALTERNATIVE(XRSTOR, \
+ XRSTORS, X86_FEATURE_XSAVES) \
+ "\n" \
+ ".pushsection .fixup,\"ax\"\n" \
+ "3: movl $-1, %[err]\n" \
+ "jmp 663b\n" \
+ ".popsection\n" \
+ _ASM_EXTABLE(661b, 3b) \
+ : [err] "=r" (err) \
+ : "D" (st), "m" (*st), "a" (lmask), "d" (hmask) \
+ : "memory")
+
+
/*
* This function is called only during boot time when x86 caps are not set
* up and alternative can not be used yet.
@@ -77,20 +122,11 @@ static inline int xsave_state_booting(struct xsave_struct *fx, u64 mask)
u32 hmask = mask >> 32;
int err = 0;

- WARN_ON(system_state != SYSTEM_BOOTING);
-
- if (boot_cpu_has(X86_FEATURE_XSAVES))
- asm volatile("1:"XSAVES"\n\t"
- "2:\n\t"
- xstate_fault
- : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
- : "memory");
+ if (static_cpu_has_safe(X86_FEATURE_XSAVES))
+ XSTATE_OP(XSAVES, fx, lmask, hmask, err);
else
- asm volatile("1:"XSAVE"\n\t"
- "2:\n\t"
- xstate_fault
- : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
- : "memory");
+ XSTATE_OP(XSAVE, fx, lmask, hmask, err);
+
return err;
}
...

To be continued...

--
Regards/Gruss,
Boris.

ECO tip #101: Trim your mails when you reply.
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