Commit 72a6c08c authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Borislav Petkov
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121456.897372712@linutronix.de
parent 0e8c54f6

arch/x86/include/asm/pkru.h

+4 −13
Original line number Diff line number Diff line
@@ -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)

arch/x86/include/asm/special_insns.h

+1 −13
Original line number Diff line number Diff line
@@ -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

arch/x86/kvm/x86.c

+2 −2
Original line number Diff line number Diff line
@@ -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)) {