On 05/11/18 18:34, James Morse wrote:
> Hi Marc,
>
> On 05/11/2018 14:36, Marc Zyngier wrote:
>> Early versions of Cortex-A76 can end-up with corrupt TLBs if they
>> speculate an AT instruction in during a guest switch while the
>
> (in during?)
>
>> S1/S2 system registers are in an inconsistent state.
>>
>> Work around it by:
>> - Mandating VHE
>> - Make sure that S1 and S2 system registers are consistent before
>> clearing HCR_EL2.TGE, which allows AT to target the EL1 translation
>> regime
>>
>> These two things together ensure that we cannot hit this erratum.
>
>
>> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
>> index 51d5d966d9e5..322109183853 100644
>> --- a/arch/arm64/kvm/hyp/switch.c
>> +++ b/arch/arm64/kvm/hyp/switch.c
>> @@ -143,6 +143,13 @@ static void deactivate_traps_vhe(void)
>> {
>> extern char vectors[]; /* kernel exception vectors */
>> write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);
>> +
>> + /*
>> + * ARM erratum 1165522 requires the actual execution of the
>> + * above before we can switch to the host translation regime.
>> + */
>> + asm(ALTERNATIVE("nop", "isb", ARM64_WORKAROUND_1165522));
>> +
>
> Host regime too ... does __tlb_switch_to_host_vhe() need the same
> treatment? It writes vttbr_el2 and hcr_el2 back to back.
It turns out that our VHE TLB invalidation are a tiny bit broken, and
that's before we work around this very erratum.
You're perfectly right that we're mitting an ISB in
__tlb_switch_to_host_vhe(). We also have the problem that we can
perfectly take an interrupt here, and maybe schedule another process
from there (very unlikely, but I couldn't fully convince myself that it
couldn't happen).
What I'm planning to do is to make these TLB invalidation sequence
atomic by disabling interrupts. Yes, this is quite a hammer, but that'
no different from !VHE, and that's a very rare event anyway.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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