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SubjectRe: [PATCH 4/6] x86/fpu/xstate: Introduce XSAVES supervisor states
On Wed, Sep 25, 2019 at 08:10:20AM -0700, Yu-cheng Yu wrote:
> Enable XSAVES supervisor states by setting MSR_IA32_XSS bits according to
> CPUID enumeration results. Also revise comments at various places.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>

Same issue as before.

> Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> ---
> arch/x86/kernel/fpu/xstate.c | 30 ++++++++++++++++++++----------
> 1 file changed, 20 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index b7f2808dd3f4..a183c319d808 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -233,13 +233,14 @@ void fpu__init_cpu_xstate(void)
> * states can be set here.
> */
> xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask_user());
> +
> + /*
> + * MSR_IA32_XSS sets supervisor states managed by XSAVES.
> + */
> + if (boot_cpu_has(X86_FEATURE_XSAVES))
> + wrmsrl(MSR_IA32_XSS, xfeatures_mask_supervisor());
> }
>
> -/*
> - * Note that in the future we will likely need a pair of
> - * functions here: one for user xstates and the other for
> - * system xstates. For now, they are the same.
> - */
> static int xfeature_enabled(enum xfeature xfeature)
> {
> return !!(xfeatures_mask_all & (1UL << xfeature));
> @@ -623,9 +624,6 @@ static void do_extra_xstate_size_checks(void)
> * the size of the *user* states. If we use it to size a buffer
> * that we use 'XSAVES' on, we could potentially overflow the
> * buffer because 'XSAVES' saves system states too.
> - *
> - * Note that we do not currently set any bits on IA32_XSS so
> - * 'XCR0 | IA32_XSS == XCR0' for now.
> */
> static unsigned int __init get_xsaves_size(void)
> {
> @@ -748,7 +746,11 @@ void __init fpu__init_system_xstate(void)
> cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
> xfeatures_mask_all = eax + ((u64)edx << 32);
>
> - /* Place supervisor features in xfeatures_mask_all here */
> + /*
> + * Find supervisor xstates supported by the processor.
> + */
> + cpuid_count(XSTATE_CPUID, 1, &eax, &ebx, &ecx, &edx);
> + xfeatures_mask_all |= ecx + ((u64)edx << 32);
>
> if ((xfeatures_mask_user() & XFEATURE_MASK_FPSSE) != XFEATURE_MASK_FPSSE) {
> /*
> @@ -788,9 +790,10 @@ void __init fpu__init_system_xstate(void)
> setup_xstate_comp();
> print_xstate_offset_size();
>
> - pr_info("x86/fpu: Enabled xstate features 0x%llx: user 0x%llx, context size is %d bytes, using '%s' format.\n",
> + pr_info("x86/fpu: Enabled xstate features 0x%llx: user 0x%llx and supervisor %llx, context size is %d bytes, using '%s' format.\n",
> xfeatures_mask_all,
> xfeatures_mask_user(),
> + xfeatures_mask_supervisor(),

So if you're dumping both user and supervisor, then you don't need to
dump _all anymore. Do it this way:

pr_info("x86/fpu: Enabled xstate features: (U: 0x%llx, S: 0x%llx), context size: %d bytes, using '%s' format.\n",
xfeatures_mask_user(),
xfeatures_mask_supervisor(),

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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