Re: [PATCH V4 2/2] riscv: add RISC-V Svpbmt extension supports

From: Jisheng Zhang
Date: Mon Nov 29 2021 - 08:46:10 EST

On Mon, 29 Nov 2021 09:40:07 +0800
wefu@xxxxxxxxxx wrote:

> From: Wei Fu <wefu@xxxxxxxxxx>
>
> This patch follows the standard pure RISC-V Svpbmt extension in
> privilege spec to solve the non-coherent SOC dma synchronization
> issues.
>
> Here is 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 high bit is already
> allocated (as the N bit), so bits [62:61] are used as the MT (aka
> MemType) field. This field specifies one of three memory types that
> are close equivalents (or equivalent in effect) to the three main x86
> and ARMv8 memory types - as shown in the following table.
>
> RISC-V
> Encoding &
> 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
>
> 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
> (__svpbmt) as _PAGE_MASK/IO/NOCACHE for pgprot_noncached
> (&writecombine) in pgtable.h. We also add _PAGE_CHG_MASK to filter
> PFN than before.
>
> Enable it in devicetree - (Add "riscv,svpbmt" in the mmu of cpu node)
> - mmu:
> riscv,svpmbt
>
> Signed-off-by: Wei Fu <wefu@xxxxxxxxxx>
> Co-developed-by: Liu Shaohua <liush@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Liu Shaohua <liush@xxxxxxxxxxxxxxxxx>
> Co-developed-by: Guo Ren <guoren@xxxxxxxxxx>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> Cc: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Anup Patel <anup.patel@xxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Atish Patra <atish.patra@xxxxxxx>
> Cc: Drew Fustini <drew@xxxxxxxxxxxxxxx>
> Cc: Wei Fu <wefu@xxxxxxxxxx>
> Cc: Wei Wu <lazyparser@xxxxxxxxx>
> Cc: Chen-Yu Tsai <wens@xxxxxxxx>
> Cc: Maxime Ripard <maxime@xxxxxxxxxx>
> Cc: Daniel Lustig <dlustig@xxxxxxxxxx>
> Cc: Greg Favor <gfavor@xxxxxxxxxxxxxxxx>
> Cc: Andrea Mondelli <andrea.mondelli@xxxxxxxxxx>
> Cc: Jonathan Behrens <behrensj@xxxxxxx>
> Cc: Xinhaoqu (Freddie) <xinhaoqu@xxxxxxxxxx>
> Cc: Bill Huffman <huffman@xxxxxxxxxxx>
> Cc: Nick Kossifidis <mick@xxxxxxxxxxxx>
> Cc: Allen Baum <allen.baum@xxxxxxxxxxxxxxxxx>
> Cc: Josh Scheid <jscheid@xxxxxxxxxxxxxxxx>
> Cc: Richard Trauben <rtrauben@xxxxxxxxx>
> ---
> arch/riscv/include/asm/fixmap.h | 2 +-
> arch/riscv/include/asm/pgtable-64.h | 21 ++++++++++++---
> arch/riscv/include/asm/pgtable-bits.h | 39 +++++++++++++++++++++++++--
> arch/riscv/include/asm/pgtable.h | 39 ++++++++++++++++++++-------
> arch/riscv/kernel/cpufeature.c | 35 ++++++++++++++++++++++++
> arch/riscv/mm/init.c | 5 ++++
> 6 files changed, 126 insertions(+), 15 deletions(-)
>
> diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
> index 54cbf07fb4e9..5acd99d08e74 100644
> --- a/arch/riscv/include/asm/fixmap.h
> +++ b/arch/riscv/include/asm/fixmap.h
> @@ -43,7 +43,7 @@ enum fixed_addresses {
> __end_of_fixed_addresses
> };
>
> -#define FIXMAP_PAGE_IO PAGE_KERNEL
> +#define FIXMAP_PAGE_IO PAGE_IOREMAP
>
> #define __early_set_fixmap __set_fixmap
>
> diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
> index 228261aa9628..16d251282b1d 100644
> --- a/arch/riscv/include/asm/pgtable-64.h
> +++ b/arch/riscv/include/asm/pgtable-64.h
> @@ -59,14 +59,29 @@ static inline void pud_clear(pud_t *pudp)
> set_pud(pudp, __pud(0));
> }
>
> +static inline unsigned long _chg_of_pmd(pmd_t pmd)
> +{
> + return (pmd_val(pmd) & _PAGE_CHG_MASK);
> +}
> +
> +static inline unsigned long _chg_of_pud(pud_t pud)
> +{
> + return (pud_val(pud) & _PAGE_CHG_MASK);
> +}
> +
> +static inline unsigned long _chg_of_pte(pte_t pte)
> +{
> + return (pte_val(pte) & _PAGE_CHG_MASK);
> +}
> +
> static inline pmd_t *pud_pgtable(pud_t pud)
> {
> - return (pmd_t *)pfn_to_virt(pud_val(pud) >> _PAGE_PFN_SHIFT);
> + return (pmd_t *)pfn_to_virt(_chg_of_pud(pud) >> _PAGE_PFN_SHIFT);
> }
>
> static inline struct page *pud_page(pud_t pud)
> {
> - return pfn_to_page(pud_val(pud) >> _PAGE_PFN_SHIFT);
> + return pfn_to_page(_chg_of_pud(pud) >> _PAGE_PFN_SHIFT);
> }
>
> static inline pmd_t pfn_pmd(unsigned long pfn, pgprot_t prot)
> @@ -76,7 +91,7 @@ static inline pmd_t pfn_pmd(unsigned long pfn, pgprot_t prot)
>
> static inline unsigned long _pmd_pfn(pmd_t pmd)
> {
> - return pmd_val(pmd) >> _PAGE_PFN_SHIFT;
> + return _chg_of_pmd(pmd) >> _PAGE_PFN_SHIFT;
> }
>
> #define mk_pmd(page, prot) pfn_pmd(page_to_pfn(page), prot)
> diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h
> index 2ee413912926..e5b0fce4ddc5 100644
> --- a/arch/riscv/include/asm/pgtable-bits.h
> +++ b/arch/riscv/include/asm/pgtable-bits.h
> @@ -7,7 +7,7 @@
> #define _ASM_RISCV_PGTABLE_BITS_H
>
> /*
> - * PTE format:
> + * rv32 PTE format:
> * | XLEN-1 10 | 9 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0
> * PFN reserved for SW D A G U X W R V
> */
> @@ -24,6 +24,40 @@
> #define _PAGE_DIRTY (1 << 7) /* Set by hardware on any write */
> #define _PAGE_SOFT (1 << 8) /* Reserved for software */
>
> +#if !defined(__ASSEMBLY__) && defined(CONFIG_64BIT)
> +/*
> + * 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 _SVPBMT_PMA 0UL
> +#define _SVPBMT_NC (1UL << 61)
> +#define _SVPBMT_IO (1UL << 62)
> +#define _SVPBMT_MASK (_SVPBMT_NC | _SVPBMT_IO)
> +
> +extern struct __svpbmt_struct {
> + unsigned long mask;
> + unsigned long pma;
> + unsigned long nocache;
> + unsigned long io;
> +} __svpbmt __cacheline_aligned;
> +
> +#define _PAGE_MASK __svpbmt.mask
> +#define _PAGE_PMA __svpbmt.pma
> +#define _PAGE_NOCACHE __svpbmt.nocache
> +#define _PAGE_IO __svpbmt.io
> +#else
> +#define _PAGE_MASK 0
> +#define _PAGE_PMA 0
> +#define _PAGE_NOCACHE 0
> +#define _PAGE_IO 0
> +#endif /* !__ASSEMBLY__ && CONFIG_64BIT */
> +
> #define _PAGE_SPECIAL _PAGE_SOFT
> #define _PAGE_TABLE _PAGE_PRESENT
>
> @@ -38,7 +72,8 @@
> /* Set of bits to preserve across pte_modify() */
> #define _PAGE_CHG_MASK (~(unsigned long)(_PAGE_PRESENT | _PAGE_READ | \
> _PAGE_WRITE | _PAGE_EXEC | \
> - _PAGE_USER | _PAGE_GLOBAL))
> + _PAGE_USER | _PAGE_GLOBAL | \
> + _PAGE_MASK))
> /*
> * when all of R/W/X are zero, the PTE is a pointer to the next level
> * of the page table; otherwise, it is a leaf PTE.
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index bf204e7c1f74..0f7a6541015f 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -138,7 +138,8 @@
> | _PAGE_PRESENT \
> | _PAGE_ACCESSED \
> | _PAGE_DIRTY \
> - | _PAGE_GLOBAL)
> + | _PAGE_GLOBAL \
> + | _PAGE_PMA)
>
> #define PAGE_KERNEL __pgprot(_PAGE_KERNEL)
> #define PAGE_KERNEL_READ __pgprot(_PAGE_KERNEL & ~_PAGE_WRITE)
> @@ -148,11 +149,9 @@
>
> #define PAGE_TABLE __pgprot(_PAGE_TABLE)
>
> -/*
> - * 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_MASK) | _PAGE_IO)
> +
> +#define PAGE_IOREMAP __pgprot(_PAGE_IOREMAP)
>
> extern pgd_t swapper_pg_dir[];
>
> @@ -232,12 +231,12 @@ static inline unsigned long _pgd_pfn(pgd_t pgd)
>
> static inline struct page *pmd_page(pmd_t pmd)
> {
> - return pfn_to_page(pmd_val(pmd) >> _PAGE_PFN_SHIFT);
> + return pfn_to_page(_chg_of_pmd(pmd) >> _PAGE_PFN_SHIFT);
> }
>
> static inline unsigned long pmd_page_vaddr(pmd_t pmd)
> {
> - return (unsigned long)pfn_to_virt(pmd_val(pmd) >> _PAGE_PFN_SHIFT);
> + return (unsigned long)pfn_to_virt(_chg_of_pmd(pmd) >> _PAGE_PFN_SHIFT);
> }
>
> static inline pte_t pmd_pte(pmd_t pmd)
> @@ -253,7 +252,7 @@ static inline pte_t pud_pte(pud_t pud)
> /* Yields the page frame number (PFN) of a page table entry */
> static inline unsigned long pte_pfn(pte_t pte)
> {
> - return (pte_val(pte) >> _PAGE_PFN_SHIFT);
> + return (_chg_of_pte(pte) >> _PAGE_PFN_SHIFT);
> }
>
> #define pte_page(x) pfn_to_page(pte_pfn(x))
> @@ -492,6 +491,28 @@ 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_MASK;
> + prot |= _PAGE_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_MASK;
> + prot |= _PAGE_NOCACHE;
> +
> + return __pgprot(prot);
> +}
> +
> /*
> * THP functions
> */
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index d959d207a40d..fa7480cb8b87 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -8,6 +8,7 @@
>
> #include <linux/bitmap.h>
> #include <linux/of.h>
> +#include <linux/pgtable.h>
> #include <asm/processor.h>
> #include <asm/hwcap.h>
> #include <asm/smp.h>
> @@ -59,6 +60,38 @@ bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, int bit)
> }
> EXPORT_SYMBOL_GPL(__riscv_isa_extension_available);
>
> +static void __init mmu_supports_svpbmt(void)
> +{
> +#if defined(CONFIG_MMU) && defined(CONFIG_64BIT)

IIRC, Christoph suggested a CONFIG_RISCV_SVPBMT when reviewing v3. What
about that idea?

> + 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 + 6, "none", 4))
> + continue;
> +
> + if (of_property_read_string(node, "mmu", &str))
> + continue;
> +
> + if (strncmp(str + 6, "svpmbt", 6))
> + continue;
> + }
> +
> + __svpbmt.pma = _SVPBMT_PMA;
> + __svpbmt.nocache = _SVPBMT_NC;
> + __svpbmt.io = _SVPBMT_IO;
> + __svpbmt.mask = _SVPBMT_MASK;
> +#endif
> +}
> +
> +static void __init mmu_supports(void)

can we remove this function currently? Instead, directly call
mmu_supports_svpbmt()?

> +{
> + mmu_supports_svpbmt();
> +}
> +
> void __init riscv_fill_hwcap(void)
> {
> struct device_node *node;
> @@ -67,6 +100,8 @@ void __init riscv_fill_hwcap(void)
> size_t i, j, isa_len;
> static unsigned long isa2hwcap[256] = {0};
>
> + mmu_supports();
> +
> isa2hwcap['i'] = isa2hwcap['I'] = COMPAT_HWCAP_ISA_I;
> isa2hwcap['m'] = isa2hwcap['M'] = COMPAT_HWCAP_ISA_M;
> isa2hwcap['a'] = isa2hwcap['A'] = COMPAT_HWCAP_ISA_A;
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 24b2b8044602..e4e658165ee1 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -854,3 +854,8 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
> return vmemmap_populate_basepages(start, end, node, NULL);
> }
> #endif
> +
> +#if defined(CONFIG_64BIT)
> +struct __svpbmt_struct __svpbmt __ro_after_init;

Added the structure for all RV64 including NOMMU case and those platforms
which doen't want SVPBMT at all, I believe Christoph's CONFIG_RISCV_SVPBMT
suggestion can solve this problem.

> +EXPORT_SYMBOL(__svpbmt);
> +#endif