[patch V2 51/52] x86/pkru: Remove xstate fiddling from write_pkru()

Thomas Gleixner
2021-06-14T16:40:56Z

The PKRU value of a task is stored in task->thread.pkru when the task is
scheduled out. PKRU is restored on schedule in from there. So keeping the
XSAVE buffer up to date is a pointless exercise.

Remove the xstate fiddling and cleanup all related functions.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/include/asm/pkru.h | 17 ++++-------------
arch/x86/include/asm/special_insns.h | 14 +-------------
arch/x86/kvm/x86.c | 4 ++--
3 files changed, 7 insertions(+), 28 deletions(-)

--- a/arch/x86/include/asm/pkru.h
+++ b/arch/x86/include/asm/pkru.h
@@ -41,23 +41,14 @@ static inline u32 read_pkru(void)

static inline void write_pkru(u32 pkru)
{
- struct pkru_state *pk;
-
if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
return;
-
- pk = get_xsave_addr(&current->thread.fpu.state.xsave, XFEATURE_PKRU);
-
/*
- * The PKRU value in xstate needs to be in sync with the value that is
- * written to the CPU. The FPU restore on return to userland would
- * otherwise load the previous value again.
+ * WRPKRU is relatively expensive compared to RDPKRU.
+ * Avoid WRPKRU when it would not change the value.
*/
- fpregs_lock();
- if (pk)
- pk->pkru = pkru;
- __write_pkru(pkru);
- fpregs_unlock();
+ if (pkru != rdpkru())
+ wrpkru(pkru);
}

static inline void pkru_write_default(void)
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -104,25 +104,13 @@ static inline void wrpkru(u32 pkru)
: : "a" (pkru), "c"(ecx), "d"(edx));
}

-static inline void __write_pkru(u32 pkru)
-{
- /*
- * WRPKRU is relatively expensive compared to RDPKRU.
- * Avoid WRPKRU when it would not change the value.
- */
- if (pkru == rdpkru())
- return;
-
- wrpkru(pkru);
-}
-
#else
static inline u32 rdpkru(void)
{
return 0;
}

-static inline void __write_pkru(u32 pkru)
+static inline void wrpkru(u32 pkru)
{
}
#endif
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -943,7 +943,7 @@ void kvm_load_guest_xsave_state(struct k
(kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
(vcpu->arch.xcr0 & XFEATURE_MASK_PKRU)) &&
vcpu->arch.pkru != vcpu->arch.host_pkru)
- __write_pkru(vcpu->arch.pkru);
+ write_pkru(vcpu->arch.pkru);
}
EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);

@@ -957,7 +957,7 @@ void kvm_load_host_xsave_state(struct kv
(vcpu->arch.xcr0 & XFEATURE_MASK_PKRU))) {
vcpu->arch.pkru = rdpkru();
if (vcpu->arch.pkru != vcpu->arch.host_pkru)
- __write_pkru(vcpu->arch.host_pkru);
+ write_pkru(vcpu->arch.host_pkru);
}

if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE)) {