Re: [RFC] syscall calling convention, stts/clts, and xstate latency

[Hans Rosenfeld <hans.rosenfeld@amd.com>]

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On Mon, Jul 25, 2011 at 05:44:32AM -0400, Andrew Lutomirski wrote:
> On Mon, Jul 25, 2011 at 2:38 AM, Ingo Molnar <mingo@elte.hu> wrote:
> > I should have mentioned it earlier, but there's a certain amount of
> > delazying patches in the tip:x86/xsave branch:
> >
> >  $ gll linus..x86/xsave
> >  300c6120b465: x86, xsave: fix non-lazy allocation of the xsave area
> >  f79018f2daa9: Merge branch 'x86/urgent' into x86/xsave
> >  66beba27e8b5: x86, xsave: remove lazy allocation of xstate area
> >  1039b306b1c6: x86, xsave: add kernel support for AMDs Lightweight Profiling (LWP)
> >  4182a4d68bac: x86, xsave: add support for non-lazy xstates
> >  324cbb83e215: x86, xsave: more cleanups
> >  2efd67935eb7: x86, xsave: remove unused code
> >  0c11e6f1aed1: x86, xsave: cleanup fpu/xsave signal frame setup
> >  7f4f0a56a7d3: x86, xsave: rework fpu/xsave support
> >  26bce4e4c56f: x86, xsave: cleanup fpu/xsave support
> >
> > it's not in tip:master because the LWP bits need (much) more work to
> > be palatable - but we could spin them off and complete them as per
> > your suggestions if they are an independent speedup on modern CPUs.
> 
> Hans, what's the status of these?  I want to do some other cleanups
> (now or in a couple of weeks) that will probably conflict with your
> xsave work.

I know of one bug in there that occasionally causes panics at boot, see
the attached patch for a fix.


Hans


-- 
%SYSTEM-F-ANARCHISM, The operating system has been overthrown

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>From 599d3ee9a9e743377739480a8a893582f1409a8d Mon Sep 17 00:00:00 2001
From: Hans Rosenfeld <hans.rosenfeld@amd.com>
Date: Wed, 6 Jul 2011 16:31:19 +0200
Subject: [PATCH 1/1] x86, xsave: clear pre-allocated xsave area

Bogus data in the xsave area can cause xrstor to panic, so make sure
that the pre-allocated xsave area is all nice and clean before being
used.

Signed-off-by: Hans Rosenfeld <hans.rosenfeld@amd.com>
---
 arch/x86/kernel/process.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c5ae256..03c5ded 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -28,8 +28,15 @@ EXPORT_SYMBOL_GPL(task_xstate_cachep);
 
 int arch_prealloc_fpu(struct task_struct *tsk)
 {
-	if (!fpu_allocated(&tsk->thread.fpu))
-		return fpu_alloc(&tsk->thread.fpu);
+	if (!fpu_allocated(&tsk->thread.fpu)) {
+		int err = fpu_alloc(&tsk->thread.fpu);
+
+		if (err)
+			return err;
+
+		fpu_clear(&tsk->thread.fpu);
+	}
+
 	return 0;
 }
 
-- 
1.5.6.5