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4109ca066b
The original purpose of XSTATE_RESERVE was to carve out space to store all of the possible extended state components that get saved with the XSAVE instruction(s). However, we are now almost entirely dynamically allocating the buffers we use for XSAVE by placing them at the end of the task_struct and them sizing them at boot. The one exception for that is the init_task. The maximum extended state component size that we have today is on systems with space for AVX-512 and Memory Protection Keys: 2696 bytes. We have reserved a PAGE_SIZE buffer in the init_task via fpregs_state->__padding. This check ensures that even if the component sizes or layout were changed (which we do not expect), that we will still not overflow the init_task's buffer. In the case that we detect we might overflow the buffer, we completely disable XSAVE support in the kernel and try to boot as if we had 'legacy x87 FPU' support in place. This is a crippled state without any of the XSAVE-enabled features (MPX, AVX, etc...). But, it at least let us boot safely. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: dave@sr71.net Cc: linux-kernel@vger.kernel.org Link: http://lkml.kernel.org/r/20150902233125.D948D475@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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