On 08/05/2024 12:34, Alexandre Ghiti wrote:
> The core mm code expects to be able to extract the pfn from a pte. NAPOT
> mappings work differently since its ptes actually point to the first pfn
> of the mapping, the other bits being used to encode the size of the
> mapping.
>
> So modify ptep_get() so that it returns a pte value that contains the
> *real* pfn (which is then different from what the HW expects) and right
> before storing the ptes to the page table, reset the pfn LSBs to the
> size of the mapping.
Did you consider leaving the pte as is and instead modifying your pte_pfn()
implementation?
For arm64 at least, it is beneficial to keep the pte marked as contiguous when
passing it up to core-mm because there are other helpers which need to parse the
contiguous bit (e.g. pte_leaf_size()). If we were to clear the cont bit in
ptep_get() that info would be lost and perf_get_pgtable_size() would always
conclude the leaf size is 4K even when it is actually 64K.
>
> And make sure that all NAPOT mappings are set using set_ptes().
>
> Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> ---
> arch/riscv/include/asm/pgtable-64.h | 11 +++
> arch/riscv/include/asm/pgtable.h | 105 ++++++++++++++++++++++++++--
> arch/riscv/mm/hugetlbpage.c | 38 +++++-----
> 3 files changed, 128 insertions(+), 26 deletions(-)
>
> diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
> index 221a5c1ee287..9fe076fc503e 100644
> --- a/arch/riscv/include/asm/pgtable-64.h
> +++ b/arch/riscv/include/asm/pgtable-64.h
> @@ -106,6 +106,17 @@ enum napot_cont_order {
> #define napot_cont_mask(order) (~(napot_cont_size(order) - 1UL))
> #define napot_pte_num(order) BIT(order)
>
> +static inline bool is_napot_order(unsigned int order)
> +{
> + unsigned int napot_order;
> +
> + for_each_napot_order(napot_order)
> + if (order == napot_order)
> + return true;
> +
> + return false;
> +}
> +
> #ifdef CONFIG_RISCV_ISA_SVNAPOT
> #define HUGE_MAX_HSTATE (2 + (NAPOT_ORDER_MAX - NAPOT_CONT_ORDER_BASE))
> #else
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 9f8ea0e33eb1..268c828f5152 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -297,6 +297,8 @@ static inline unsigned long pte_napot(pte_t pte)
> return pte_val(pte) & _PAGE_NAPOT;
> }
>
> +#define pte_valid_napot(pte) (pte_present(pte) && pte_napot(pte))
> +
> static inline pte_t pte_mknapot(pte_t pte, unsigned int order)
> {
> int pos = order - 1 + _PAGE_PFN_SHIFT;
> @@ -306,6 +308,12 @@ static inline pte_t pte_mknapot(pte_t pte, unsigned int order)
> return __pte((pte_val(pte) & napot_mask) | napot_bit | _PAGE_NAPOT);
> }
>
> +/* pte at entry must *not* encode the mapping size in the pfn LSBs. */
> +static inline pte_t pte_clear_napot(pte_t pte)
> +{
> + return __pte(pte_val(pte) & ~_PAGE_NAPOT);
> +}
> +
> #else
>
> static __always_inline bool has_svnapot(void) { return false; }
> @@ -315,17 +323,14 @@ static inline unsigned long pte_napot(pte_t pte)
> return 0;
> }
>
> +#define pte_valid_napot(pte) false
> +
> #endif /* CONFIG_RISCV_ISA_SVNAPOT */
>
> /* Yields the page frame number (PFN) of a page table entry */
> static inline unsigned long pte_pfn(pte_t pte)
> {
> - unsigned long res = __page_val_to_pfn(pte_val(pte));
> -
> - if (has_svnapot() && pte_napot(pte))
> - res = res & (res - 1UL);
> -
> - return res;
> + return __page_val_to_pfn(pte_val(pte));
> }
>
> #define pte_page(x) pfn_to_page(pte_pfn(x))
> @@ -525,9 +530,91 @@ static inline void __set_pte_at(struct mm_struct *mm, pte_t *ptep, pte_t pteval)
>
> #define PFN_PTE_SHIFT _PAGE_PFN_SHIFT
>
> +#ifdef CONFIG_RISCV_ISA_SVNAPOT
> +static inline int arch_contpte_get_num_contig(pte_t *ptep, unsigned long size,
> + size_t *pgsize)
> +{
> + pte_t __pte;
> +
> + /* We must read the raw value of the pte to get the size of the mapping */
> + __pte = READ_ONCE(*ptep);
> +
> + if (pgsize) {
> + if (size >= PGDIR_SIZE)
> + *pgsize = PGDIR_SIZE;
> + else if (size >= P4D_SIZE)
> + *pgsize = P4D_SIZE;
> + else if (size >= PUD_SIZE)
> + *pgsize = PUD_SIZE;
> + else if (size >= PMD_SIZE)
> + *pgsize = PMD_SIZE;
> + else
> + *pgsize = PAGE_SIZE;
> + }
> +
> + /* Make sure __pte is not a swap entry */
> + if (pte_valid_napot(__pte))
> + return napot_pte_num(napot_cont_order(__pte));
> +
> + return 1;
> +}
> +#endif
> +
> +static inline pte_t ptep_get(pte_t *ptep)
> +{
> + pte_t pte = READ_ONCE(*ptep);
> +
> +#ifdef CONFIG_RISCV_ISA_SVNAPOT
> + /*
> + * The pte we load has the N bit set and the size of the mapping in
> + * the pfn LSBs: keep the N bit and replace the mapping size with
> + * the *real* pfn since the core mm code expects to find it there.
> + * The mapping size will be reset just before being written to the
> + * page table in set_ptes().
> + */
> + if (unlikely(pte_valid_napot(pte))) {
> + unsigned int order = napot_cont_order(pte);
> + int pos = order - 1 + _PAGE_PFN_SHIFT;
> + unsigned long napot_mask = ~GENMASK(pos, _PAGE_PFN_SHIFT);
> + pte_t *orig_ptep = PTR_ALIGN_DOWN(ptep, sizeof(*ptep) * napot_pte_num(order));
> +
> + pte = __pte((pte_val(pte) & napot_mask) + ((ptep - orig_ptep) << _PAGE_PFN_SHIFT));
> + }
> +#endif
> +
> + return pte;
> +}
> +#define ptep_get ptep_get
> +
> static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
> pte_t *ptep, pte_t pteval, unsigned int nr)
> {
> +#ifdef CONFIG_RISCV_ISA_SVNAPOT
> + if (unlikely(pte_valid_napot(pteval))) {
> + unsigned int order = ilog2(nr);
> +
> + if (!is_napot_order(order)) {
> + /*
> + * Something's weird, we are given a NAPOT pte but the
> + * size of the mapping is not a known NAPOT mapping
> + * size, so clear the NAPOT bit and map this without
> + * NAPOT support: core mm only manipulates pte with the
> + * real pfn so we know the pte is valid without the N
> + * bit.
> + */
> + pr_err("Incorrect NAPOT mapping, resetting.\n");
> + pteval = pte_clear_napot(pteval);
> + } else {
> + /*
> + * NAPOT ptes that arrive here only have the N bit set
> + * and their pfn does not contain the mapping size, so
> + * set that here.
> + */
> + pteval = pte_mknapot(pteval, order);
> + }
> + }
> +#endif
I think all this complexity comes along due to using this function both as a
public interface that the core-mm uses (which never sets napot) and also using
it as an internal interface that riscv-hugetlb uses (which does set napot)? It
might be more understandable if you layer it into a lower level/internal API and
a higher level/public API (similar to arm64)?
> +
> page_table_check_ptes_set(mm, ptep, pteval, nr);
>
> for (;;) {
> @@ -535,6 +622,12 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
> if (--nr == 0)
> break;
> ptep++;
> +
> +#ifdef CONFIG_RISCV_ISA_SVNAPOT
> + if (unlikely(pte_valid_napot(pteval)))
> + continue;
> +#endif
> +
> pte_val(pteval) += 1 << _PAGE_PFN_SHIFT;
> }
> }
> diff --git a/arch/riscv/mm/hugetlbpage.c b/arch/riscv/mm/hugetlbpage.c
> index 5ef2a6891158..fe8067ee71b4 100644
> --- a/arch/riscv/mm/hugetlbpage.c
> +++ b/arch/riscv/mm/hugetlbpage.c
> @@ -256,8 +256,7 @@ void set_huge_pte_at(struct mm_struct *mm,
>
> clear_flush(mm, addr, ptep, pgsize, pte_num);
>
> - for (i = 0; i < pte_num; i++, ptep++, addr += pgsize)
> - set_pte_at(mm, addr, ptep, pte);
> + set_ptes(mm, addr, ptep, pte, pte_num);
> }
>
> int huge_ptep_set_access_flags(struct vm_area_struct *vma,
> @@ -267,16 +266,16 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
> int dirty)
> {
> struct mm_struct *mm = vma->vm_mm;
> - unsigned long order;
> + size_t pgsize;
> pte_t orig_pte;
> - int i, pte_num;
> + int pte_num;
>
> if (!pte_napot(pte))
> return ptep_set_access_flags(vma, addr, ptep, pte, dirty);
>
> - order = napot_cont_order(pte);
> - pte_num = napot_pte_num(order);
> - ptep = huge_pte_offset(mm, addr, napot_cont_size(order));
> + pte_num = arch_contpte_get_num_contig(ptep, 0, &pgsize);
> + ptep = huge_pte_offset(mm, addr, pte_num * pgsize);
> +
> orig_pte = get_clear_contig_flush(mm, addr, ptep, pte_num);
>
> if (pte_dirty(orig_pte))
> @@ -285,8 +284,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
> if (pte_young(orig_pte))
> pte = pte_mkyoung(pte);
>
> - for (i = 0; i < pte_num; i++, addr += PAGE_SIZE, ptep++)
> - set_pte_at(mm, addr, ptep, pte);
> + set_ptes(mm, addr, ptep, pte, pte_num);
>
> return true;
> }
> @@ -301,7 +299,7 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
> if (!pte_napot(orig_pte))
> return ptep_get_and_clear(mm, addr, ptep);
>
> - pte_num = napot_pte_num(napot_cont_order(orig_pte));
> + pte_num = arch_contpte_get_num_contig(ptep, 0, NULL);
>
> return get_clear_contig(mm, addr, ptep, pte_num);
> }
> @@ -311,24 +309,23 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm,
> pte_t *ptep)
> {
> pte_t pte = ptep_get(ptep);
> - unsigned long order;
> + size_t pgsize;
> pte_t orig_pte;
> - int i, pte_num;
> + int pte_num;
>
> if (!pte_napot(pte)) {
> ptep_set_wrprotect(mm, addr, ptep);
> return;
> }
>
> - order = napot_cont_order(pte);
> - pte_num = napot_pte_num(order);
> - ptep = huge_pte_offset(mm, addr, napot_cont_size(order));
> + pte_num = arch_contpte_get_num_contig(ptep, 0, &pgsize);
> + ptep = huge_pte_offset(mm, addr, pte_num * pgsize);
> +
> orig_pte = get_clear_contig_flush(mm, addr, ptep, pte_num);
>
> orig_pte = pte_wrprotect(orig_pte);
>
> - for (i = 0; i < pte_num; i++, addr += PAGE_SIZE, ptep++)
> - set_pte_at(mm, addr, ptep, orig_pte);
> + set_ptes(mm, addr, ptep, orig_pte, pte_num);
> }
>
> pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
> @@ -341,7 +338,7 @@ pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
> if (!pte_napot(pte))
> return ptep_clear_flush(vma, addr, ptep);
>
> - pte_num = napot_pte_num(napot_cont_order(pte));
> + pte_num = arch_contpte_get_num_contig(ptep, 0, NULL);
>
> return get_clear_contig_flush(vma->vm_mm, addr, ptep, pte_num);
> }
> @@ -351,6 +348,7 @@ void huge_pte_clear(struct mm_struct *mm,
> pte_t *ptep,
> unsigned long sz)
> {
> + size_t pgsize;
> pte_t pte = ptep_get(ptep);
> int i, pte_num;
>
> @@ -359,8 +357,8 @@ void huge_pte_clear(struct mm_struct *mm,
> return;
> }
>
> - pte_num = napot_pte_num(napot_cont_order(pte));
> - for (i = 0; i < pte_num; i++, addr += PAGE_SIZE, ptep++)
> + pte_num = arch_contpte_get_num_contig(ptep, 0, &pgsize);
> + for (i = 0; i < pte_num; i++, addr += pgsize, ptep++)
> pte_clear(mm, addr, ptep);
> }
>
