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Date:   Thu, 25 Apr 2019 10:42:45 -0700 (PDT)
Subject:     Re: [PATCH v2 2/2] riscv: Introduce huge page support for 32/64bit kernel
In-Reply-To: <20190409061449.5083-3-alex@ghiti.fr>
CC:     Christoph Hellwig <hch@infradead.org>, mike.kravetz@oracle.com,
        catalin.marinas@arm.com, Will Deacon <will.deacon@arm.com>,
        aou@eecs.berkeley.edu, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, hpa@zytor.com, x86@kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-riscv@lists.infradead.org, alex@ghiti.fr
From:   Palmer Dabbelt <palmer@sifive.com>
To:     alex@ghiti.fr
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On Mon, 08 Apr 2019 23:14:49 PDT (-0700), alex@ghiti.fr wrote:
> This patch implements both 4MB huge page support for 32bit kernel
> and 2MB/1GB huge pages support for 64bit kernel.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
>  arch/riscv/Kconfig               |  8 ++++++
>  arch/riscv/include/asm/hugetlb.h | 18 +++++++++++++
>  arch/riscv/include/asm/page.h    | 10 ++++++++
>  arch/riscv/include/asm/pgtable.h |  8 ++++--
>  arch/riscv/mm/Makefile           |  2 ++
>  arch/riscv/mm/hugetlbpage.c      | 44 ++++++++++++++++++++++++++++++++
>  6 files changed, 88 insertions(+), 2 deletions(-)
>  create mode 100644 arch/riscv/include/asm/hugetlb.h
>  create mode 100644 arch/riscv/mm/hugetlbpage.c
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index eb56c82d8aa1..a400d4b4e1b3 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -49,6 +49,8 @@ config RISCV
>  	select GENERIC_IRQ_MULTI_HANDLER
>  	select ARCH_HAS_PTE_SPECIAL
>  	select HAVE_EBPF_JIT if 64BIT
> +	select ARCH_HAS_GIGANTIC_PAGE
> +	select ARCH_WANT_HUGE_PMD_SHARE if 64BIT
>
>  config MMU
>  	def_bool y
> @@ -63,6 +65,12 @@ config PAGE_OFFSET
>  	default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
>  	default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
>
> +config ARCH_WANT_GENERAL_HUGETLB
> +	def_bool y
> +
> +config SYS_SUPPORTS_HUGETLBFS
> +	def_bool y
> +
>  config STACKTRACE_SUPPORT
>  	def_bool y
>
> diff --git a/arch/riscv/include/asm/hugetlb.h b/arch/riscv/include/asm/hugetlb.h
> new file mode 100644
> index 000000000000..728a5db66597
> --- /dev/null
> +++ b/arch/riscv/include/asm/hugetlb.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_RISCV_HUGETLB_H
> +#define _ASM_RISCV_HUGETLB_H
> +
> +#include <asm-generic/hugetlb.h>
> +#include <asm/page.h>
> +
> +static inline int is_hugepage_only_range(struct mm_struct *mm,
> +					 unsigned long addr,
> +					 unsigned long len) {
> +	return 0;
> +}
> +
> +static inline void arch_clear_hugepage_flags(struct page *page)
> +{
> +}
> +
> +#endif /* _ASM_RISCV_HUGETLB_H */
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 2a546a52f02a..4ef2936295aa 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -24,6 +24,16 @@
>  #define PAGE_SIZE	(_AC(1, UL) << PAGE_SHIFT)
>  #define PAGE_MASK	(~(PAGE_SIZE - 1))
>
> +#ifdef CONFIG_64BIT
> +#define HUGE_MAX_HSTATE		2
> +#else
> +#define HUGE_MAX_HSTATE		1
> +#endif
> +#define HPAGE_SHIFT		PMD_SHIFT
> +#define HPAGE_SIZE		(_AC(1, UL) << HPAGE_SHIFT)
> +#define HPAGE_MASK              (~(HPAGE_SIZE - 1))
> +#define HUGETLB_PAGE_ORDER      (HPAGE_SHIFT - PAGE_SHIFT)
> +
>  /*
>   * PAGE_OFFSET -- the first address of the first page of memory.
>   * When not using MMU this corresponds to the first free page in
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 1141364d990e..f3456fcdff92 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -121,7 +121,6 @@ static inline void pmd_clear(pmd_t *pmdp)
>  	set_pmd(pmdp, __pmd(0));
>  }
>
> -
>  static inline pgd_t pfn_pgd(unsigned long pfn, pgprot_t prot)
>  {
>  	return __pgd((pfn << _PAGE_PFN_SHIFT) | pgprot_val(prot));
> @@ -258,6 +257,11 @@ static inline pte_t pte_mkspecial(pte_t pte)
>  	return __pte(pte_val(pte) | _PAGE_SPECIAL);
>  }
>
> +static inline pte_t pte_mkhuge(pte_t pte)
> +{
> +	return pte;
> +}
> +
>  /* Modify page protection bits */
>  static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>  {
> @@ -417,7 +421,7 @@ static inline void pgtable_cache_init(void)
>  #define VMALLOC_START    (PAGE_OFFSET - VMALLOC_SIZE)
>
>  /*
> - * Task size is 0x40000000000 for RV64 or 0xb800000 for RV32.
> + * Task size is 0x4000000000 for RV64 or 0xb800000 for RV32.
>   * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
>   */
>  #ifdef CONFIG_64BIT
> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> index b68aac701803..7bbe533d92f5 100644
> --- a/arch/riscv/mm/Makefile
> +++ b/arch/riscv/mm/Makefile
> @@ -9,3 +9,5 @@ obj-y += fault.o
>  obj-y += extable.o
>  obj-y += ioremap.o
>  obj-y += cacheflush.o
> +
> +obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
> diff --git a/arch/riscv/mm/hugetlbpage.c b/arch/riscv/mm/hugetlbpage.c
> new file mode 100644
> index 000000000000..0d4747e9d5b5
> --- /dev/null
> +++ b/arch/riscv/mm/hugetlbpage.c
> @@ -0,0 +1,44 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/hugetlb.h>
> +#include <linux/err.h>
> +
> +int pud_huge(pud_t pud)
> +{
> +	return pud_present(pud) &&
> +		(pud_val(pud) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC));
> +}
> +
> +int pmd_huge(pmd_t pmd)
> +{
> +	return pmd_present(pmd) &&
> +		(pmd_val(pmd) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC));
> +}
> +
> +static __init int setup_hugepagesz(char *opt)
> +{
> +	unsigned long ps = memparse(opt, &opt);
> +
> +	if (ps == HPAGE_SIZE) {
> +		hugetlb_add_hstate(HPAGE_SHIFT - PAGE_SHIFT);
> +	} else if (IS_ENABLED(CONFIG_64BIT) && ps == PUD_SIZE) {
> +		hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
> +	} else {
> +		hugetlb_bad_size();
> +		pr_err("hugepagesz: Unsupported page size %lu M\n", ps >> 20);
> +		return 0;
> +	}
> +
> +	return 1;
> +}
> +__setup("hugepagesz=", setup_hugepagesz);
> +
> +#ifdef CONFIG_CONTIG_ALLOC
> +static __init int gigantic_pages_init(void)
> +{
> +	/* With CONTIG_ALLOC, we can allocate gigantic pages at runtime */
> +	if (IS_ENABLED(CONFIG_64BIT) && !size_to_hstate(1UL << PUD_SHIFT))
> +		hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
> +	return 0;
> +}
> +arch_initcall(gigantic_pages_init);
> +#endif

I'm getting some build errors when this is applied to 5.1-c6.  I think all I've
done is turn on hugetlb:

    $ diff -u arch/riscv/configs/defconfig defconfig
    --- arch/riscv/configs/defconfig        2019-04-24 16:23:39.027994174 -0700
    +++ defconfig   2019-04-25 10:39:34.722544413 -0700
    @@ -5,6 +5,7 @@
     CONFIG_CGROUPS=y
     CONFIG_CGROUP_SCHED=y
     CONFIG_CFS_BANDWIDTH=y
    +CONFIG_CGROUP_HUGETLB=y
     CONFIG_CGROUP_BPF=y
     CONFIG_NAMESPACES=y
     CONFIG_USER_NS=y
    @@ -72,6 +73,7 @@
     CONFIG_VFAT_FS=y
     CONFIG_TMPFS=y
     CONFIG_TMPFS_POSIX_ACL=y
    +CONFIG_HUGETLBFS=y
     CONFIG_NFS_FS=y
     CONFIG_NFS_V4=y
     CONFIG_NFS_V4_1=y