On 2019-02-25 10:08:10 [-0800], Dave Hansen wrote:
> On 2/21/19 3:50 AM, Sebastian Andrzej Siewior wrote:
> > @@ -111,6 +111,12 @@ static inline void __write_pkru(u32 pkru)
> > {
> > u32 ecx = 0, edx = 0;
> >
> > + /*
> > + * WRPKRU is relatively expensive compared to RDPKRU.
> > + * Avoid WRPKRU when it would not change the value.
> > + */
> > + if (pkru == __read_pkru())
> > + return;
> > /*
> > * "wrpkru" instruction. Loads contents in EAX to PKRU,
> > * requires that ecx = edx = 0.
>
> Could we do this in write_pkru() instead? I tried to keep the __
> versions of read and write as simple and symmetric as possible.
write_pkru() has:
| static inline void write_pkru(u32 pkru)
| {
| struct pkru_state *pk;
|
| if (!boot_cpu_has(X86_FEATURE_OSPKE))
| return;
|
| pk = get_xsave_addr(¤t->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.
| */
| fpregs_lock();
| if (pk)
| pk->pkru = pkru;
| __write_pkru(pkru);
| fpregs_unlock();
| }
and is other callers besides write_pkru():
|arch/x86/include/asm/fpu/internal.h: __write_pkru(pkru_val);
|arch/x86/kvm/vmx/vmx.c: __write_pkru(vcpu->arch.pkru);
|arch/x86/kvm/vmx/vmx.c: __write_pkru(vmx->host_pkru)
Do want __write_pkru_isn() and __read_pkru_isn() so those are symmetric
and then we would have __write_pkru() which does the read check and
invokes __write_pkru_isn()?
Sebastian
