Re: [RFC PATCH 1/2] arm64: kvm: Save/restore MTE registers

[Steven Price]

On 17/06/2020 15:05, Catalin Marinas wrote:
> On Wed, Jun 17, 2020 at 01:38:43PM +0100, Steven Price wrote:
> > diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> > index 75b1925763f1..6ecee1528566 100644
> > --- a/arch/arm64/kvm/hyp/sysreg-sr.c
> > +++ b/arch/arm64/kvm/hyp/sysreg-sr.c
> > @@ -26,6 +26,12 @@
> >   static void __hyp_text __sysreg_save_common_state(struct kvm_cpu_context *ctxt)
> >   {
> >   	ctxt->sys_regs[MDSCR_EL1]	= read_sysreg(mdscr_el1);
> > +	if (system_supports_mte()) {
> > +		ctxt->sys_regs[RGSR_EL1] = read_sysreg_s(SYS_RGSR_EL1);
> > +		ctxt->sys_regs[GCR_EL1] = read_sysreg_s(SYS_GCR_EL1);
> > +		ctxt->sys_regs[TFSRE0_EL1] = read_sysreg_s(SYS_TFSRE0_EL1);
> > +		ctxt->sys_regs[TFSR_EL1] = read_sysreg_s(SYS_TFSR_EL1);
> > +	}
>
> TFSR_EL1 is not a common register as we have the TFSR_EL2 as well. So
> you'd have to access it as read_sysreg_el1(SYS_TFSR) so that, in the VHE
> case, it generates TFSR_EL12, otherwise you just save the host register.

Ah, thanks for pointing that out - I'd got myself confused with the 
whole VHE _EL12 registers. I'd managed to miss that TFSR is banked.

> Also, since TFSR*_EL1 can be set asynchronously, I think we need to set
> the SCTLR_EL2.ITFSB bit so that the register update is synchronised on
> entry to EL2. With VHE we get this automatically as part of
> SCTLR_EL1_SET but it turns out that we have another SCTLR_ELx_FLAGS
> macro for the non-VHE case (why not calling this SCTLR_EL2_* I have no
> idea).

I hadn't noticed that there was a different set for the non-VHE case 
which was missing ITFSB - I'll update that.

Thanks,

Steve

> >   	/*
> >   	 * The host arm64 Linux uses sp_el0 to point to 'current' and it must
> > @@ -99,6 +105,12 @@ NOKPROBE_SYMBOL(sysreg_save_guest_state_vhe);
> >   static void __hyp_text __sysreg_restore_common_state(struct kvm_cpu_context *ctxt)
> >   {
> >   	write_sysreg(ctxt->sys_regs[MDSCR_EL1],	  mdscr_el1);
> > +	if (system_supports_mte()) {
> > +		write_sysreg_s(ctxt->sys_regs[RGSR_EL1], SYS_RGSR_EL1);
> > +		write_sysreg_s(ctxt->sys_regs[GCR_EL1], SYS_GCR_EL1);
> > +		write_sysreg_s(ctxt->sys_regs[TFSRE0_EL1], SYS_TFSRE0_EL1);
> > +		write_sysreg_s(ctxt->sys_regs[TFSR_EL1], SYS_TFSR_EL1);
> > +	}
>
> Similarly here, you override the TFSR_EL2 with VHE enabled.