Messages in this thread | | | Date | Sat, 01 Feb 2014 15:40:13 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] Make math_state_restore() save and restore the interrupt flag |
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On 02/01/2014 01:17 PM, George Spelvin wrote: >> .. which *does* actually bring up something that might work, and might >> be a good idea: remove the "restore math state or set TS" from the >> normal kernel paths *entirely*, and move it to the "return to user >> space" phase. > > This definitely seems much more sensible. For processors without > optimized context save/restore, the decision whether to restore eagerly > is best made once the kernel has decided what it's returning *to*. > > From an interrupt handler, there are now three cases: > 1) FPU not in use, available for immediate use. > 2) FPU in use by user-space; save to <location> before using. > 3) FPU in use by kernel code; may not be used (unless we want > to add nested FPU state save hair). >
OK, let's circle back for a bit. We have an active bug, and we clearly have a lot of restructuring that could/should be done. We need to fix the bug first; if we're going to a bunch of restructuring then that ought to be separate. The first bit is how we fix the immediate bug.
-hpa
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