Commit-ID: 1f96b1efbad4bb753e7fd265753f6cac1cdc5648 Gitweb: http://git.kernel.org/tip/1f96b1efbad4bb753e7fd265753f6cac1cdc5648 Author: Dave Hansen <[email protected]> AuthorDate: Fri, 12 Feb 2016 13:01:58 -0800 Committer: Ingo Molnar <[email protected]> CommitDate: Tue, 16 Feb 2016 10:11:13 +0100
x86/fpu: Add placeholder for 'Processor Trace' XSAVE state There is an XSAVE state component for Intel Processor Trace (PT). But, we do not currently use it. We add a placeholder in the code for it so it is not a mystery and also so we do not need an explicit enum initialization for Protection Keys in a moment. Why don't we use it? We might end up using this at _some_ point in the future. But, this is a "system" state which requires using the currently unsupported XSAVES feature. Unlike all the other XSAVE states, PT state is also not directly tied to a thread. You might context-switch between threads, but not want to change any of the PT state. Or, you might switch between threads, and *do* want to change PT state, all depending on what is being traced. We currently just manually set some MSRs to do this PT context switching, and it is unclear whether replacing our direct MSR use with XSAVE will be a net win or loss, both in code complexity and performance. Signed-off-by: Dave Hansen <[email protected]> Reviewed-by: Thomas Gleixner <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Rik van Riel <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/include/asm/fpu/types.h | 1 + arch/x86/kernel/fpu/xstate.c | 10 ++++++++-- 2 files changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h index 1c6f6ac..aad3181 100644 --- a/arch/x86/include/asm/fpu/types.h +++ b/arch/x86/include/asm/fpu/types.h @@ -108,6 +108,7 @@ enum xfeature { XFEATURE_OPMASK, XFEATURE_ZMM_Hi256, XFEATURE_Hi16_ZMM, + XFEATURE_PT_UNIMPLEMENTED_SO_FAR, XFEATURE_MAX, }; diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index d425cda5..c2e2349 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -13,6 +13,11 @@ #include <asm/tlbflush.h> +/* + * Although we spell it out in here, the Processor Trace + * xfeature is completely unused. We use other mechanisms + * to save/restore PT state in Linux. + */ static const char *xfeature_names[] = { "x87 floating point registers" , @@ -23,7 +28,7 @@ static const char *xfeature_names[] = "AVX-512 opmask" , "AVX-512 Hi256" , "AVX-512 ZMM_Hi256" , - "unknown xstate feature" , + "Processor Trace (unused)" , }; /* @@ -470,7 +475,8 @@ static void check_xstate_against_struct(int nr) * numbers. */ if ((nr < XFEATURE_YMM) || - (nr >= XFEATURE_MAX)) { + (nr >= XFEATURE_MAX) || + (nr == XFEATURE_PT_UNIMPLEMENTED_SO_FAR)) { WARN_ONCE(1, "no structure for xstate: %d\n", nr); XSTATE_WARN_ON(1); }
