From: Ingo Molnar Date: Wed, 20 May 2015 09:45:30 +0000 (+0200) Subject: x86/fpu: Disable XSAVES* support for now X-Git-Tag: omap-for-v4.2/wakeirq-drivers-v2^2~2^2~49^2 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e88221c50cadade0eb4f7f149f4967d760212695;p=pandora-kernel.git x86/fpu: Disable XSAVES* support for now The kernel's handling of 'compacted' xsave state layout is buggy: http://marc.info/?l=linux-kernel&m=142967852317199 I don't have such a system, and the description there is vague, but from extrapolation I guess that there were two kinds of bugs observed: - boot crashes, due to size calculations being wrong and the dynamic allocation allocating a too small xstate area. (This is now fixed in the new FPU code - but still present in stable kernels.) - FPU state corruption and ABI breakage: if signal handlers try to change the FPU state in standard format, which then the kernel tries to restore in the compacted format. These breakages are scary, but they only occur on a small number of systems that have XSAVES* CPU support. Yet we have had XSAVES support in the upstream kernel for a large number of stable kernel releases, and the fixes are involved and unproven. So do the safe resolution first: disable XSAVES* support and only use the standard xstate format. This makes the code work and is easy to backport. On top of this we can work on enabling (and testing!) proper compacted format support, without backporting pressure, on top of the new, cleaned up FPU code. Cc: Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed