[PATCH v2 3/8] x86/fpu/xstate: Introduce XSAVES supervisor states

Yu-cheng Yu
2020-01-21T20:20:08Z

Enable XSAVES supervisor states by setting MSR_IA32_XSS bits according to
CPUID enumeration results. Also revise comments at various places.

v2:
- Remove printing of supervisor xstates from fpu__init_system_xstate().

Co-developed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
---
arch/x86/kernel/fpu/xstate.c | 27 ++++++++++++++++++---------
1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 3b22d630f5bb..0c5c91ee235e 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -229,13 +229,14 @@ 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));
@@ -626,9 +627,6 @@ 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)
{
@@ -751,7 +749,11 @@ 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) {
/*
@@ -812,6 +814,13 @@ void fpu__resume_cpu(void)
*/
if (boot_cpu_has(X86_FEATURE_XSAVE))
xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask_user());
+
+ /*
+ * Restore IA32_XSS. The same CPUID bit enumerates support
+ * of XSAVES and MSR_IA32_XSS.
+ */
+ if (boot_cpu_has(X86_FEATURE_XSAVES))
+ wrmsrl(MSR_IA32_XSS, xfeatures_mask_supervisor());
}

/*
--
2.21.0