Messages in this thread Patch in this message | | | From | Guo Ren <> | Date | Tue, 2 Nov 2021 10:07:58 +0800 | Subject | Re: [RESEND PATCH V3 0/2] riscv: add RISC-V Svpbmt Standard Extension supports |
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On Wed, Oct 27, 2021 at 8:12 AM Palmer Dabbelt <palmerdabbelt@google.com> 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. Don't worry about that, I've compiled the Linux with the patch and below modification in k210_nommu_defconfig. Passed
diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h index 3b38fe14f169..b4bb41337fdc 100644 --- a/arch/riscv/include/asm/pgtable-bits.h +++ b/arch/riscv/include/asm/pgtable-bits.h @@ -25,7 +25,7 @@ #define _PAGE_SOFT (1 << 8) /* Reserved for software */
#ifndef __ASSEMBLY__ -#ifdef CONFIG_64BIT +#if defined(CONFIG_64BIT) && defined(CONFIG_MMU) /* * rv64 PTE format: * | 63 | 62 61 | 60 54 | 53 10 | 9 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c index d198eabe55d4..58639dfe5917 100644 --- a/arch/riscv/mm/init.c +++ b/arch/riscv/mm/init.c @@ -856,7 +856,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, } #endif
-#ifdef CONFIG_64BIT +#if defined(CONFIG_64BIT) && defined(CONFIG_MMU) struct __riscv_svpbmt_struct __riscv_svpbmt __ro_after_init; EXPORT_SYMBOL(__riscv_svpbmt);
So, I don't think the patch would affect M-mode nommu Linux. To separate MMU & no-MMU clearly, I suggest fuwei add #if defined(CONFIG_64BIT) && defined(CONFIG_MMU)
> 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 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(-)
-- Best Regards Guo Ren
ML: https://lore.kernel.org/linux-csky/
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