Re: [RFC PATCH v4 03/27] x86/fpu/xstate: Enable XSAVES system states
From: Borislav Petkov <bp@alien8.de>
Date: 2018-10-02 17:15:56
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On Fri, Sep 21, 2018 at 08:03:27AM -0700, Yu-cheng Yu wrote:
XSAVES saves both system and user states. The Linux kernel currently does not save/restore any system states. This patch creates the framework for supporting system states.
... and needs a lot more text explaining *why* it is doing that.
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Signed-off-by: Yu-cheng Yu <redacted> --- arch/x86/include/asm/fpu/internal.h | 3 +- arch/x86/include/asm/fpu/xstate.h | 9 ++- arch/x86/kernel/fpu/core.c | 7 +- arch/x86/kernel/fpu/init.c | 10 --- arch/x86/kernel/fpu/xstate.c | 112 +++++++++++++++++----------- 5 files changed, 80 insertions(+), 61 deletions(-)diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h index f1f9bf91a0ab..1f447865db3a 100644 --- a/arch/x86/include/asm/fpu/internal.h +++ b/arch/x86/include/asm/fpu/internal.h@@ -45,7 +45,6 @@ extern void fpu__init_cpu_xstate(void); extern void fpu__init_system(struct cpuinfo_x86 *c); extern void fpu__init_check_bugs(void); extern void fpu__resume_cpu(void); -extern u64 fpu__get_supported_xfeatures_mask(void); /* * Debugging facility:@@ -94,7 +93,7 @@ static inline void fpstate_init_xstate(struct xregs_state *xsave) * trigger #GP: */ xsave->header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT | - xfeatures_mask_user; + xfeatures_mask_all; } static inline void fpstate_init_fxstate(struct fxregs_state *fx)diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h index 9b382e5157ed..a32dc5f8c963 100644 --- a/arch/x86/include/asm/fpu/xstate.h +++ b/arch/x86/include/asm/fpu/xstate.h@@ -19,10 +19,10 @@ #define XSAVE_YMM_SIZE 256 #define XSAVE_YMM_OFFSET (XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET) -/* System features */ -#define XFEATURE_MASK_SYSTEM (XFEATURE_MASK_PT)
Previous patch renames it, this patch deletes it. Why do we need all that unnecessary churn? Also, this patch is trying to do a couple of things at once and reviewing it is not trivial. Please split the changes logically.
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diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 19f8df54c72a..dd2c561c4544 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c@@ -51,13 +51,16 @@ static short xsave_cpuid_features[] __initdata = { }; /* - * Mask of xstate features supported by the CPU and the kernel: + * Mask of xstate features supported by the CPU and the kernel. + * This is the result from CPUID query, SUPPORTED_XFEATURES_MASK, + * and boot_cpu_has(). */
This needs to explain what both masks are - user and system. "CPU" and "kernel" is not "user" and "all".
u64 xfeatures_mask_user __read_mostly; +u64 xfeatures_mask_all __read_mostly;
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@@ -219,30 +222,31 @@ void fpstate_sanitize_xstate(struct fpu *fpu) */ void fpu__init_cpu_xstate(void) { - if (!boot_cpu_has(X86_FEATURE_XSAVE) || !xfeatures_mask_user) + if (!boot_cpu_has(X86_FEATURE_XSAVE) || !xfeatures_mask_all) return; + + cr4_set_bits(X86_CR4_OSXSAVE); + /* - * Make it clear that XSAVES system states are not yet - * implemented should anyone expect it to work by changing - * bits in XFEATURE_MASK_* macros and XCR0. + * XCR_XFEATURE_ENABLED_MASK sets the features that are managed + * by XSAVE{C, OPT} and XRSTOR. Only XSAVE user states can be + * set here. */ - WARN_ONCE((xfeatures_mask_user & XFEATURE_MASK_SYSTEM), - "x86/fpu: XSAVES system states are not yet implemented.\n"); + xsetbv(XCR_XFEATURE_ENABLED_MASK, + xfeatures_mask_user);
No need to break the line here. Also, you have a couple more places in your patches where you unnecessarily break lines. Please don't do that, even if it exceeds 80 cols by a couple of chars.
- xfeatures_mask_user &= ~XFEATURE_MASK_SYSTEM; - - cr4_set_bits(X86_CR4_OSXSAVE); - xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask_user); + /* + * MSR_IA32_XSS sets which XSAVES system states to be managed by + * XSAVES. Only XSAVES system states can be set here. + */ + if (boot_cpu_has(X86_FEATURE_XSAVES)) + wrmsrl(MSR_IA32_XSS, + xfeatures_mask_all & ~xfeatures_mask_user);
--
Regards/Gruss,
Boris.
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