Messages in this thread | | | Date | Wed, 27 Oct 2021 09:54:16 +0200 | Subject | Re: [RESEND PATCH V3 0/2] riscv: add RISC-V Svpbmt Standard Extension supports | From | Heinrich Schuchardt <> |
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On 10/27/21 02:12, Palmer Dabbelt wrote: > On Sun, 24 Oct 2021 21:06:05 PDT (-0700), wefu@redhat.com wrote: >> From: Fu Wei <wefu@redhat.com> >> >> This patch follows the RISC-V standard Svpbmt extension in >> privilege spec to solve the non-coherent SOC DMA synchronization >> issues. >> >> The svpbmt PTE format: >> | 63 | 62-61 | 60-8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 >> N MT RSW D A G U X W R V >> ^ >> >> Of the Reserved bits [63:54] in a leaf PTE, the bits [62:61] are used as >> the MT (aka MemType) field. This field specifies one of three memory >> types >> as shown in the following table: >> MemType RISC-V Description >> ---------- ------------------------------------------------ >> 00 - PMA Normal Cacheable, No change to implied PMA memory type >> 01 - NC Non-cacheable, idempotent, weakly-ordered Main Memory >> 10 - IO Non-cacheable, non-idempotent, strongly-ordered I/O memory >> 11 - Rsvd Reserved for future standard use > > Do you have a pointer to the spec that contains these? I'm specifically > worried about these page-based attributes being elided when paging is > off (ie, M-mode), which has caused issues in systems I've worked with in > the past. I'm assuming there's something related to this in the specs, > but I'm worried we'll need some sort of ack from M-mode that it's been > setup to work that way. One could imagine an MPRV-like approach > working, but I don't see enough in the old specs and I'm having trouble > figuring out where the canonical version of this lives.
The draft version of the spec is available in chapter 6, p 87 of https://raw.githubusercontent.com/riscv/virtual-memory/main/specs/663-Svpbmt.pdf
According to https://groups.google.com/a/groups.riscv.org/g/isa-dev/c/nOrD9t9ImEw/m/tstjm4QbAAAJ review has started Sep 17th.
Best regards
Heinrich
> >> The standard protection_map[] needn't be modified because the "PMA" >> type keeps the highest bits zero. >> And the whole modification is limited in the arch/riscv/* and using >> a global variable(__riscv_svpbmt) as _PAGE_DMA_MASK/IO/NC for >> pgprot_noncached (&writecombine) in pgtable.h. >> We also add _PAGE_CHG_MASK to filter PFN than before. >> >> Enable it in devicetree - (Add "mmu-supports-svpbmt" in cpu node) >> - mmu-supports-svpbmt > > Maybe this is enough of an ack, but we'll need to have some pretty > specific documentation if that's the case. It's not described that way > in the docs right now, they just talk about CPU support (IMO we could > probe that with a trap, but I'm fine with the DT entry as it's a bit > simpler). > >> Wei Fu (2): >> dt-bindings: riscv: add mmu-supports-svpbmt for Svpbmt >> riscv: add RISC-V Svpbmt extension supports >> >> .../devicetree/bindings/riscv/cpus.yaml | 5 +++ >> arch/riscv/include/asm/fixmap.h | 2 +- >> arch/riscv/include/asm/pgtable-64.h | 8 ++-- >> arch/riscv/include/asm/pgtable-bits.h | 41 ++++++++++++++++++- >> arch/riscv/include/asm/pgtable.h | 39 ++++++++++++++---- >> arch/riscv/kernel/cpufeature.c | 32 +++++++++++++++ >> arch/riscv/mm/init.c | 5 +++ >> 7 files changed, 117 insertions(+), 15 deletions(-)
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