On Thu, Nov 23, 2017 at 07:49:29PM +0100, Christoffer Dall wrote: > On Thu, Nov 23, 2017 at 06:06:34PM +0000, Dave Martin wrote: > > > > diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S > > > > index 12ee62d..d8e8d22 100644 > > > > --- a/arch/arm64/kvm/hyp/entry.S > > > > +++ b/arch/arm64/kvm/hyp/entry.S > > > > @@ -162,37 +162,75 @@ ENTRY(__fpsimd_guest_restore) > > > > stp x2, x3, [sp, #-16]! > > > > stp x4, lr, [sp, #-16]! > > > > > > > > + mrs x0, cptr_el2 > > > > + > > > > +alternative_if_not ARM64_SVE > > > > + mov x1, #CPTR_EL2_TFP > > > > + mov x2, #CPACR_EL1_FPEN > > > > +alternative_else > > > > + mov x1, #CPTR_EL2_TFP | CPTR_EL2_TZ > > > > + mov x2, #CPACR_EL1_FPEN | CPACR_EL1_ZEN > > > > +alternative_endif > > > > + > > > > alternative_if_not ARM64_HAS_VIRT_HOST_EXTN > > > > - mrs x2, cptr_el2 > > > > - bic x2, x2, #CPTR_EL2_TFP > > > > - msr cptr_el2, x2 > > > > + bic x0, x0, x1 > > > > alternative_else > > > > - mrs x2, cpacr_el1 > > > > - orr x2, x2, #CPACR_EL1_FPEN > > > > - msr cpacr_el1, x2 > > > > + orr x0, x0, x2 > > > > alternative_endif > > > > + > > > > + msr cptr_el2, x0 > > > > isb > > > > > > > > - mrs x3, tpidr_el2 > > > > + mrs x4, tpidr_el2 > > > > > > > > - ldr x0, [x3, #VCPU_HOST_CONTEXT] > > > > + ldr x0, [x4, #VCPU_HOST_CONTEXT] > > > > kern_hyp_va x0 > > > > add x0, x0, #CPU_GP_REG_OFFSET(CPU_FP_REGS) > > > > bl __fpsimd_save_state > > > > > > > > - add x2, x3, #VCPU_CONTEXT > > > > + add x2, x4, #VCPU_CONTEXT > > > > + > > > > +#ifdef CONFIG_ARM64_SVE > > > > +alternative_if ARM64_SVE > > > > + b 2f > > > > +alternative_else_nop_endif > > > > +#endif > > > > + > > > > add x0, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS) > > > > bl __fpsimd_restore_state > > > > > > > > +0: > > > > // Skip restoring fpexc32 for AArch64 guests > > > > mrs x1, hcr_el2 > > > > tbnz x1, #HCR_RW_SHIFT, 1f > > > > - ldr x4, [x3, #VCPU_FPEXC32_EL2] > > > > - msr fpexc32_el2, x4 > > > > + ldr x3, [x4, #VCPU_FPEXC32_EL2] > > > > + msr fpexc32_el2, x3 > > > > 1: > > > > ldp x4, lr, [sp], #16 > > > > ldp x2, x3, [sp], #16 > > > > ldp x0, x1, [sp], #16 > > > > > > > > eret > > > > + > > > > +#ifdef CONFIG_ARM64_SVE > > > > +2: > > > > +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN > > > > + ldr x0, [x4, #VCPU_ZCR_EL2] > > > > + ldr x3, [x4, #VCPU_ZCR_EL1] > > > > + msr_s SYS_ZCR_EL2, x0 > > > > +alternative_else > > > > + ldr x0, [x4, #VCPU_ZCR_EL1] > > > > + ldr x3, [x4, #VCPU_ZCR_EL2] > > > > + msr_s SYS_ZCR_EL12, x0 > > > > +alternative_endif > > > > + > > > > + ldr w0, [x4, #VCPU_SVE_FFR_OFFSET] > > > > + add x0, x4, x0 > > > > + add x1, x2, #VCPU_FPSR - VCPU_CONTEXT > > > > + mov x2, x3 > > > > + bl __sve_load_state > > > > + > > > > + b 0b > > > > +#endif /* CONFIG_ARM64_SVE */ > > > > > > I think if we could move all of this out to C code that would be much > > > nicer. Also, we currently do the short-circuit fault-in-fpsimd state > > > inside hyp and always save the fpsimd state when returning to the host > > > kernel, but in my optimization series I change this to leave the state > > > in hardware until we schedule or return to userspace, so perhaps we can > > > go all the way back to handle_exit() then without much performance loss, > > > which may further simplify the SVE support? Or all the way back to VCPU RUN exiting, if Rik's proposal[*] for x86 FPU registers makes sense for these registers as well. [*] https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1536992.html > > > > This is what I would be aiming for, coupled with awareness of whether > > the host has any live FPSIMD/SVE state in the first place: for SVE > > specifically the answer will _usually_ be "no". > > > > Ideally, we would give a vcpu its own SVE/FPSIMD context on a par with > > host tasks and just reuse the fpsimd.c machinery rather than inventing > > separate machinery for KVM -- That's what I understand Rik is trying to do. > > the flipside would be that the hyp code > > may need to mainpulate thread flags etc. -- I didn't want to rush to > > this destination before learning to walk though. > > Fair enough, but then I think the "let's rely on VHE for SVE support" > comes in, because you can mostly think of hyp code as being the host > kernel code. > > > > > For the first iteration of KVM SVE support I would rather not do that > > rafactoring, to reduce the number of things I'm breaking at the same > > time... > > > > On the other hand, if it makes the SVE support code much simpler, it may > be easier in the end. It may be worth thinking of a way we can measure > the two approaches with basic FPSIMD so that we know the consequences of > refactoring anything. > > > > > > > The hit would obviously be a slightly higher latency on the first fault > > > in the guest on SVE/fpsimd. > > > > For SVE it's probably not the end of the world since that's higher > > cost to save/restore in the first place. > > > > For FPSIMD I've less of a feel for it. > > > > Yeah, me neither. We'd have to measure something. Thanks, drew _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
