Re: [PATCH] riscv: Add RISC-V svpbmt extension

[Anup Patel]

On Thu, Sep 23, 2021 at 12:57 PM <guoren@xxxxxxxxxx> wrote:
>
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>
> 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. The standard protection_map[] needn't
> be modified. So the whole modification is in the arch/riscv pgtable and
> using a global variable (__riscv_svpbmt) in the _PAGE_DMA_MASK/IO/NC
> for pgprot_noncached (&writecombine). We also need _PAGE_CHG_MASK to
> detect PFN than before.
>
> Devicetree: reuse "mmu-type" of cpu_section as a user interface to
> enable the feature or not:
>  - riscv,sv39,svpbmt
>  - riscv,sv48,svpbmt
>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> Cc: Liu Shaohua <liush@xxxxxxxxxxxxxxxxx>
> Cc: Wei Fu <wefu@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>
> ---
>  .../devicetree/bindings/riscv/cpus.yaml       |  2 +
>  arch/riscv/include/asm/fixmap.h               |  2 +-
>  arch/riscv/include/asm/pgtable-64.h           |  8 ++--
>  arch/riscv/include/asm/pgtable-bits.h         | 46 ++++++++++++++++++-
>  arch/riscv/include/asm/pgtable.h              | 39 ++++++++++++----
>  arch/riscv/include/asm/processor.h            |  1 +
>  arch/riscv/kernel/cpufeature.c                | 23 ++++++++++
>  arch/riscv/kernel/setup.c                     |  2 +
>  arch/riscv/mm/init.c                          |  5 ++
>  9 files changed, 113 insertions(+), 15 deletions(-)
>
> 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

I think augmenting the "mmu-type" DT property is a good approach but the
description of "mmu-type" DT property needs to say:

"Identifies the MMU address translation mode and page based memory
type used on ..."

Also, DT bindings change is generally a separate patch so better to make
a separate patch for this.

>
>    riscv,isa:
> 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..0b53ea67e91a 100644
> --- a/arch/riscv/include/asm/pgtable-64.h
> +++ b/arch/riscv/include/asm/pgtable-64.h
> @@ -61,12 +61,14 @@ static inline void pud_clear(pud_t *pudp)
>
>  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((pud_val(pud) & _PAGE_CHG_MASK)
> +                                               >> _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((pud_val(pud) & _PAGE_CHG_MASK)
> +                                               >> _PAGE_PFN_SHIFT);
>  }
>
>  static inline pmd_t pfn_pmd(unsigned long pfn, pgprot_t prot)
> @@ -76,7 +78,7 @@ 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 (pmd_val(pmd) & _PAGE_CHG_MASK) >> _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..041fe4fdbafa 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 +24,47 @@
>  #define _PAGE_DIRTY     (1 << 7)    /* Set by hardware on any write */
>  #define _PAGE_SOFT      (1 << 8)    /* Reserved for software */
>
> +#ifndef __ASSEMBLY__
> +#ifdef 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 _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)
> +
> +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
>
> @@ -38,7 +79,8 @@
>  /* 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_DMA_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 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)
>
>  #define PAGE_KERNEL            __pgprot(_PAGE_KERNEL)
>  #define PAGE_KERNEL_READ       __pgprot(_PAGE_KERNEL & ~_PAGE_WRITE)
> @@ -146,11 +147,9 @@
>
>  #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_DMA_MASK) | _PAGE_DMA_IO)
> +
> +#define PAGE_IOREMAP           __pgprot(_PAGE_IOREMAP)
>
>  extern pgd_t swapper_pg_dir[];
>
> @@ -230,12 +229,12 @@ 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((pmd_val(pmd) & _PAGE_CHG_MASK) >> _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((pmd_val(pmd) & _PAGE_CHG_MASK) >> _PAGE_PFN_SHIFT);
>  }
>
>  static inline pte_t pmd_pte(pmd_t pmd)
> @@ -251,7 +250,7 @@ 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 ((pte_val(pte) & _PAGE_CHG_MASK) >> _PAGE_PFN_SHIFT);
>  }
>
>  #define pte_page(x)     pfn_to_page(pte_pfn(x))
> @@ -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);
> +}
> +
>  /*
>   * THP functions
>   */
> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> index 021ed64ee608..92676156cbf6 100644
> --- a/arch/riscv/include/asm/processor.h
> +++ b/arch/riscv/include/asm/processor.h
> @@ -70,6 +70,7 @@ struct device_node;
>  int riscv_of_processor_hartid(struct device_node *node);
>  int riscv_of_parent_hartid(struct device_node *node);
>
> +extern void riscv_svpbmt(void);

You can drop this change.

>  extern void riscv_fill_hwcap(void);
>  extern int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index d959d207a40d..4a2211c2c464 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 +60,28 @@ bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, int bit)
>  }
>  EXPORT_SYMBOL_GPL(__riscv_isa_extension_available);
>
> +void __init riscv_svpbmt(void)

Make this static function and call it from riscv_fill_hwcap().

> +{
> +#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;
> +               }

I don't agree with this loop.

The __riscv_svpbmt should be updated only when all CPU nodes
have "svpmbt" in the "mmu-type" DT property.

> +       }
> +#endif
> +}
> +
>  void __init riscv_fill_hwcap(void)
>  {
>         struct device_node *node;
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 120b2f6f71bc..e7457113b45e 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -294,6 +294,8 @@ void __init setup_arch(char **cmdline_p)
>         setup_smp();
>  #endif
>
> +       riscv_svpbmt();
> +

You can drop this change based on above comment.

>         riscv_fill_hwcap();
>  }
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 7cb4f391d106..43b2e11fd3e0 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -905,3 +905,8 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>         return vmemmap_populate_basepages(start, end, node, NULL);
>  }
>  #endif
> +
> +#ifdef CONFIG_64BIT
> +struct __riscv_svpbmt_struct __riscv_svpbmt __ro_after_init;
> +EXPORT_SYMBOL(__riscv_svpbmt);
> +#endif
> --
> 2.25.1
>

Appending "svpmb" suffix to "mmu-type" breaks print_mmu()
in arch/riscv/kernel/cpu.c. Please update that as well.

We will also need couple of Tested-by for existing boards.

Regards,
Anup