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

Steven Price
2020-06-18T10:44:03Z

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.
>