Messages in this thread | | | Date | Fri, 27 Nov 2015 11:06:27 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86, fpu: fix 32-bit signal frame handling |
| |
* Dave Hansen <dave@sr71.net> wrote:
> On 11/10/2015 04:23 PM, Dave Hansen wrote: > > For MPX, this leads to the most permissive state and means we > > silently lose bounds violations. I think this would also mean > > that we could lose *ANY* FPU/SSE/AVX state. I'm not sure why > > no one has spotted this bug. > > FWIW, I looked at this a little more today. > > We lose all extended state for our "extended xfeatures", also known as > state component numbers >=2 (AVX, MPX, AVX-512, PKEYs)... But we retain > the state for FP/SSE state. So we lose the top half of the AVX > registers (the bottom half are SSE state). > > I also did a little objdump'ing and grep'ing in a 32-bit distro. > There's no sign of actual use of the ymm registers. > > Basically, it appears nobody has taken a 64-bit Sandybridge or later > CPU, put a 32-bit distro on it that had a >=3.7 kernel on it and tried > to use AVX instructions. Or, if they did, they got random corruption > and gave up before actually diagnosing the problem. :)
Weird: putting a 32-bit distro on such a fine piece of 64-bit hardware is pure masochism - and such masochism would also imply the willingness to track down random corruptions! ;-)
Thanks,
Ingo
| |