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x86/pkru: Remove xstate fiddling from write_pkru() 

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>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121456.897372712@linutronix.de
This commit is contained in:
Thomas Gleixner 2021-06-23 14:02:23 +02:00 committed by Borislav Petkov
parent 0e8c54f6b2
commit 72a6c08c44
3 changed files with 7 additions and 28 deletions
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17
arch/x86/include/asm/pkru.h
View File

@ -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)

14
arch/x86/include/asm/special_insns.h
View File

@ -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

4
arch/x86/kvm/x86.c
View File

@ -943,7 +943,7 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
(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 kvm_vcpu *vcpu)
(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)) {