Messages in this thread | | | Date | Thu, 2 Apr 2015 17:52:10 +0200 | From | Quentin Casasnovas <> | Subject | Re: [PATCH] x86/xsave: Robustify and merge macros |
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On Thu, Apr 02, 2015 at 03:11:22PM +0200, Borislav Petkov wrote: > From: Borislav Petkov <bp@suse.de> > > 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, > see > > 06c8173eb92b ("x86/fpu/xsaves: Fix improper uses of __ex_table") > > for an example. > > Add single macros which combine the alternatives and the exception > handling.
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@suse.de> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: Ingo Molnar <mingo@kernel.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com> > Cc: Oleg Nesterov <oleg@redhat.com> > Cc: Andy Lutomirski <luto@amacapital.net> > --- > 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 for XSTATE_XSAVE()/XSTATE_RESTORE().
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 test this?
Quentin
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