Messages in this thread Patch in this message | | | Date | Thu, 23 Sep 2021 12:24:13 +0300 | From | Nick Kossifidis <> | Subject | Re: [PATCH] riscv: Add RISC-V svpbmt extension |
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Hello Guo,
Στις 2021-09-23 10:27, guoren@kernel.org έγραψε: diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml index e534f6a7cfa1..1825cd8db0de 100644 --- a/Documentation/devicetree/bindings/riscv/cpus.yaml +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml @@ -56,7 +56,9 @@ properties: enum: - riscv,sv32 - riscv,sv39 + - riscv,sv39,svpbmt - riscv,sv48 + - riscv,sv48,svpbmt - riscv,none
Isn't svpbmt orthogonal to the mmu type ? It's a functionality that can be present on either sv39/48/57 so why not have another "svpbmt" property directly on the cpu node ?
> + * rv64 PTE format: > + * | 63 | 62 61 | 60 54 | 53 10 | 9 8 | 7 | 6 | 5 | 4 | > 3 | 2 | 1 | 0 > + * N MT RSV PFN reserved for SW D A G U > X W R V > + * [62:61] Memory Type definitions: > + * 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 > + */ > +#define _PAGE_MT_MASK ((u64)0x3 << 61) > +#define _PAGE_MT_PMA ((u64)0x0 << 61) > +#define _PAGE_MT_NC ((u64)0x1 << 61) > +#define _PAGE_MT_IO ((u64)0x2 << 61) > + It'd be cleaner IMHO if you defined _PAGE_MT_MASK as (_PAGE_MT_PMA | _PAGE_MT_NC | _PAGE_MT_IO), like other masks are defined (e.g. _PAGE_CHG_MASK on the same file). I also suggest you use unsigned long instead of u64 for consistency. > +enum { > + MT_PMA, > + MT_NC, > + MT_IO, > + MT_MAX > +}; > + > +extern struct __riscv_svpbmt_struct { > + unsigned long mask; > + unsigned long mt[MT_MAX]; > +} __riscv_svpbmt; > + > +#define _PAGE_DMA_MASK __riscv_svpbmt.mask > +#define _PAGE_DMA_PMA __riscv_svpbmt.mt[MT_PMA] > +#define _PAGE_DMA_NC __riscv_svpbmt.mt[MT_NC] > +#define _PAGE_DMA_IO __riscv_svpbmt.mt[MT_IO] > +#else > +#define _PAGE_DMA_MASK 0 > +#define _PAGE_DMA_PMA 0 > +#define _PAGE_DMA_NC 0 > +#define _PAGE_DMA_IO 0 > +#endif /* CONFIG_64BIT */ > +#endif /* __ASSEMBLY__ */ > + > #define _PAGE_SPECIAL _PAGE_SOFT > #define _PAGE_TABLE _PAGE_PRESENT >
This struct is not useful as part of enabling the standard Svpbmt extension on Linux, we can set _PAGE_DMA_* macros directly on this patch and introduce the struct approach later on, when we also define alternative values for _PAGE_DMA_* flags. Also to someone reading the code the struct doesn't make sense without some documentation on why it's needed. Finally why the enum / array ? Why not just have different fields on the struct ?
> diff --git a/arch/riscv/include/asm/pgtable.h > b/arch/riscv/include/asm/pgtable.h > index 39b550310ec6..d07ba586c866 100644 > --- a/arch/riscv/include/asm/pgtable.h > +++ b/arch/riscv/include/asm/pgtable.h > @@ -136,7 +136,8 @@ > | _PAGE_PRESENT \ > | _PAGE_ACCESSED \ > | _PAGE_DIRTY \ > - | _PAGE_GLOBAL) > + | _PAGE_GLOBAL \ > + | _PAGE_DMA_PMA) >
That's a bit misleading, it's like marking the kernel pages as DMAable.
-/* - * The RISC-V ISA doesn't yet specify how to query or modify PMAs, so we can't - * change the properties of memory regions. - */ -#define _PAGE_IOREMAP _PAGE_KERNEL +#define _PAGE_IOREMAP ((_PAGE_KERNEL & ~_PAGE_DMA_MASK) | _PAGE_DMA_IO) + +#define PAGE_IOREMAP __pgprot(_PAGE_IOREMAP) This isn't used anywhere.
@@ -490,6 +489,28 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma, return ptep_test_and_clear_young(vma, address, ptep); } +#define pgprot_noncached pgprot_noncached +static inline pgprot_t pgprot_noncached(pgprot_t _prot) +{ + unsigned long prot = pgprot_val(_prot); + + prot &= ~_PAGE_DMA_MASK; + prot |= _PAGE_DMA_IO; + + return __pgprot(prot); +} + +#define pgprot_writecombine pgprot_writecombine +static inline pgprot_t pgprot_writecombine(pgprot_t _prot) +{ + unsigned long prot = pgprot_val(_prot); + + prot &= ~_PAGE_DMA_MASK; + prot |= _PAGE_DMA_NC; + + return __pgprot(prot); +} + We also have the IO type, we should also define pgprot_device to also ensure ordering, or else it'll fallback to pgprot_noncached, which in our case won't work well due to RVWMO: https://elixir.bootlin.com/linux/latest/source/include/linux/pgtable.h#L930
+void __init riscv_svpbmt(void) +{ +#ifdef CONFIG_64BIT + struct device_node *node; + const char *str; + + for_each_of_cpu_node(node) { + if (of_property_read_string(node, "mmu-type", &str)) { + continue; + } + + if (!strncmp(str + 11, "svpbmt", 6)) { + __riscv_svpbmt.mask = _PAGE_MT_MASK; + __riscv_svpbmt.mt[MT_PMA] = _PAGE_MT_PMA; + __riscv_svpbmt.mt[MT_NC] = _PAGE_MT_NC; + __riscv_svpbmt.mt[MT_IO] = _PAGE_MT_IO; + break; + } + } +#endif +} You break; here the first time you find a cpu node with svpbmt enabled, shouldn't we make sure that all used cpu nodes support svpbmt before using the extension ?
Regards, Nick
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