On 9 November 2015 at 09:00, Heyi Guo <heyi....@linaro.org> wrote:
> Hi All,
>
> In AARCH64 MMU configuration code, sharable attribute will be set to inner
> sharable when memory attribute is write back. However, I have 2 questions
> about this code:
> 1. Why is it set to inner sharable only when memory attribute is write back?
> Either write through or uncached will use non-shareable for TCR.
> 2. All memory regions will be set to none shareable in AARCH64 MMU
> configuration code, whatever cachable attribute they have (WB, WT or UC). In
> my opinion, TCR attribute should be kept consistent with the memory where
> translation tables are located, i.e. TCR_SH_NON_SHAREABLE will always be the
> proper attribute for TCR.
>
> So could you help to confirm whether there is anything wrong with the code?
>
You are right: this is incorrect. Leo Duran of AMD contributed a patch
at some point that addressed this, I think, but I don't know what
happened to it.
We could probably get away with using inner shareable for all mappings
(since uncached mappings are treated as outer shareable anyway), but
for correctness, let's set everything explicitly.
Then, the TCR bits should just reflect the shareability of the mappings.
I will cook up a patch in a minute.
Did you observe any actual issues? Or did you find this by code inspection only?
Thanks,
Ard.
> ArmPkg/Library/ArmLib/AArch64/AArch64Mmu.c
>
>
> if ((TranslationTableAttribute ==
> ARM_MEMORY_REGION_ATTRIBUTE_UNCACHED_UNBUFFERED) ||
> (TranslationTableAttribute ==
> ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_UNCACHED_UNBUFFERED)) {
> TCR |= TCR_SH_NON_SHAREABLE | TCR_RGN_OUTER_NON_CACHEABLE |
> TCR_RGN_INNER_NON_CACHEABLE;
> } else if ((TranslationTableAttribute ==
> ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK) ||
> (TranslationTableAttribute ==
> ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_BACK)) {
>
> ++ TCR |= **TCR_SH_INNER_SHAREABLE** | TCR_RGN_OUTER_WRITE_BACK_ALLOC |
> TCR_RGN_INNER_WRITE_BACK_ALLOC;
>
>
> } else if ((TranslationTableAttribute ==
> ARM_MEMORY_REGION_ATTRIBUTE_WRITE_THROUGH) ||
> (TranslationTableAttribute ==
> ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_THROUGH)) {
> TCR |= TCR_SH_NON_SHAREABLE | TCR_RGN_OUTER_WRITE_THROUGH |
> TCR_RGN_INNER_WRITE_THROUGH;
>
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