Re: [Qemu-devel] [PATCH 0/4] target/arm: Minimize TLB flushing for ASID changes

[Peter Maydell]

On 29 October 2018 at 15:53, Richard Henderson
<address@hidden> wrote:
> In http://lists.nongnu.org/archive/html/qemu-devel/2018-10/msg04181.html
> (already upstream) I added a check for ASID changes without realizing
> that TTBCR_EL1 has the A1 bit, controlling which register actually
> contains the active ASID.
>
> In http://lists.nongnu.org/archive/html/qemu-devel/2018-10/msg04182.html
> I suggested a set of mmu_idx to flush when the ASID does change.  In
> follow-up, Peter suggested more.
>
> I now choose secure vs non-secure mmu_idx based on which register is being
> modified, not the current state of the cpu.  Unless I am mistaken, secure
> state can write to the non-secure registers.  Which means that the current
> state of the cpu is irrelevant and only the register matters.
>
> Peter suggested flushing S1E3 when changing ttbr0_s.  I can see how this
> is overlapped onto the EL3 (Secure Monitor) state, but I cannot see how
> the ASID is used from EL3.  The best evidence I can find for this is that
> there is no TLBIASID* register that is applicable to flushing EL3; that's
> not conclusive proof though.  So while I'm not sure it's necessary, I'm
> also not sure it isn't necessary, and so I've included S1E3 in the flush.
>
> I now also use the VMID to conditionally invalidate the stage 2 translation
> state.  This shows how I anticipaged @depmap to be used in patch 1.

Hi; just a note that I'm deferring this series to 4.0, so may
not get to reviewing it for a bit.

thanks
-- PMM