[PATCH v9 04/26] x86/fpu/xstate: Add a new variable to indicate dynamic user states

Chang S. Bae
2021-07-30T15:06:15Z

The XSTATE per-task buffer is in preparation to be dynamic for user states.
Introduce a new mask variable to indicate the 'dynamic' user states. The
value is determined at boot-time.

No functional change.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
Changes from v5:
* Made the variable __ro_after_init.
* Dropped the perf's xstate buffer renaming, as renamed already.

Changes from v3:
* Updated the changelog. (Borislav Petkov)
* Updated the code comment. (Borislav Petkov)

Changes from v2:
* Updated the changelog for clarification.
---
arch/x86/include/asm/fpu/xstate.h | 2 ++
arch/x86/kernel/fpu/xstate.c | 9 +++++++++
2 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index 2451bccc6cac..bc4cba62906b 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -129,6 +129,8 @@ static inline u64 xfeatures_mask_independent(void)
return XFEATURE_MASK_INDEPENDENT;
}

+extern u64 xfeatures_mask_user_dynamic;
+
extern u64 xstate_fx_sw_bytes[USER_XSTATE_FX_SW_WORDS];

extern void __init update_regset_xstate_info(unsigned int size,
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index d9c029ab9497..74e608c6ad6c 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -62,6 +62,12 @@ static short xsave_cpuid_features[] __initdata = {
u64 xfeatures_mask_all __ro_after_init;
EXPORT_SYMBOL_GPL(xfeatures_mask_all);

+/*
+ * This represents user xstates, a subset of xfeatures_mask_all, saved in a
+ * dynamic kernel XSAVE buffer.
+ */
+u64 xfeatures_mask_user_dynamic __ro_after_init;
+
static unsigned int xstate_offsets[XFEATURE_MAX] __ro_after_init =
{ [ 0 ... XFEATURE_MAX - 1] = -1};
static unsigned int xstate_sizes[XFEATURE_MAX] __ro_after_init =
@@ -709,6 +715,7 @@ static int __init init_xstate_size(void)
static void fpu__init_disable_system_xstate(void)
{
xfeatures_mask_all = 0;
+ xfeatures_mask_user_dynamic = 0;
cr4_clear_bits(X86_CR4_OSXSAVE);
setup_clear_cpu_cap(X86_FEATURE_XSAVE);
}
@@ -780,6 +787,8 @@ void __init fpu__init_system_xstate(void)

/* Store it for paranoia check at the end */
xfeatures = xfeatures_mask_all;
+ /* Do not support the dynamically allocated buffer yet. */
+ xfeatures_mask_user_dynamic = 0;

/* Enable xstate instructions to be able to continue with initialization: */
fpu__init_cpu_xstate();
--
2.17.1