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Re: [PATCH 1/4] target/arm: Don't use a TLB for ARMMMUIdx_Stage2

From: Richard Henderson
Subject: Re: [PATCH 1/4] target/arm: Don't use a TLB for ARMMMUIdx_Stage2
Date: Wed, 29 Apr 2020 11:39:40 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0

On 3/30/20 2:03 PM, Peter Maydell wrote:
> We define ARMMMUIdx_Stage2 as being an MMU index which uses a QEMU
> TLB.  However we never actually use the TLB -- all stage 2 lookups
> are done by direct calls to get_phys_addr_lpae() followed by a
> physical address load via address_space_ld*().
> Remove Stage2 from the list of ARM MMU indexes which correspond to
> real core MMU indexes, and instead put it in the set of "NOTLB" ARM
> MMU indexes.
> This allows us to drop NB_MMU_MODES to 11.  It also means we can
> safely add support for the ARMv8.3-TTS2UXN extension, which adds
> permission bits to the stage 2 descriptors which define execute
> permission separatel for EL0 and EL1; supporting that while keeping
> Stage2 in a QEMU TLB would require us to use separate TLBs for
> "Stage2 for an EL0 access" and "Stage2 for an EL1 access", which is a
> lot of extra complication given we aren't even using the QEMU TLB.
> In the process of updating the comment on our MMU index use,
> fix a couple of other minor errors:
>  * NS EL2 EL2&0 was missing from the list in the comment
>  * some text hadn't been updated from when we bumped NB_MMU_MODES
>    above 8
> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  target/arm/cpu-param.h |   2 +-
>  target/arm/cpu.h       |  21 +++++---
>  target/arm/helper.c    | 112 ++++-------------------------------------
>  3 files changed, 27 insertions(+), 108 deletions(-)

Reviewed-by: Richard Henderson <address@hidden>


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