Re: [PATCH v2 02/34] s390: Use _pt_s390_gaddr for gmap address tracking

Mike Rapoport
2023-05-25T08:58:59Z

On Mon, May 01, 2023 at 12:27:57PM -0700, Vishal Moola (Oracle) wrote:
> s390 uses page->index to keep track of page tables for the guest address
> space. In an attempt to consolidate the usage of page fields in s390,
> replace _pt_pad_2 with _pt_s390_gaddr to replace page->index in gmap.
>
> This will help with the splitting of struct ptdesc from struct page, as
> well as allow s390 to use _pt_frag_refcount for fragmented page table
> tracking.
>
> Since page->_pt_s390_gaddr aliases with mapping, ensure its set to NULL
> before freeing the pages as well.

Wouldn't it be easier to use _pt_pad_1 which is aliased with lru and that
does not seem to be used by page tables at all?

> This also reverts commit 7e25de77bc5ea ("s390/mm: use pmd_pgtable_page()
> helper in __gmap_segment_gaddr()") which had s390 use
> pmd_pgtable_page() to get a gmap page table, as pmd_pgtable_page()
> should be used for more generic process page tables.
>
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
> ---
> arch/s390/mm/gmap.c | 56 +++++++++++++++++++++++++++-------------
> include/linux/mm_types.h | 2 +-
> 2 files changed, 39 insertions(+), 19 deletions(-)
>
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index dfe905c7bd8e..a9e8b1805894 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -70,7 +70,7 @@ static struct gmap *gmap_alloc(unsigned long limit)
> page = alloc_pages(GFP_KERNEL_ACCOUNT, CRST_ALLOC_ORDER);
> if (!page)
> goto out_free;
> - page->index = 0;
> + page->_pt_s390_gaddr = 0;
> list_add(&page->lru, &gmap->crst_list);
> table = page_to_virt(page);
> crst_table_init(table, etype);
> @@ -187,16 +187,20 @@ static void gmap_free(struct gmap *gmap)
> if (!(gmap_is_shadow(gmap) && gmap->removed))
> gmap_flush_tlb(gmap);
> /* Free all segment & region tables. */
> - list_for_each_entry_safe(page, next, &gmap->crst_list, lru)
> + list_for_each_entry_safe(page, next, &gmap->crst_list, lru) {
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> + }
> gmap_radix_tree_free(&gmap->guest_to_host);
> gmap_radix_tree_free(&gmap->host_to_guest);
>
> /* Free additional data for a shadow gmap */
> if (gmap_is_shadow(gmap)) {
> /* Free all page tables. */
> - list_for_each_entry_safe(page, next, &gmap->pt_list, lru)
> + list_for_each_entry_safe(page, next, &gmap->pt_list, lru) {
> + page->_pt_s390_gaddr = 0;
> page_table_free_pgste(page);
> + }
> gmap_rmap_radix_tree_free(&gmap->host_to_rmap);
> /* Release reference to the parent */
> gmap_put(gmap->parent);
> @@ -318,12 +322,14 @@ static int gmap_alloc_table(struct gmap *gmap, unsigned long *table,
> list_add(&page->lru, &gmap->crst_list);
> *table = __pa(new) | _REGION_ENTRY_LENGTH |
> (*table & _REGION_ENTRY_TYPE_MASK);
> - page->index = gaddr;
> + page->_pt_s390_gaddr = gaddr;
> page = NULL;
> }
> spin_unlock(&gmap->guest_table_lock);
> - if (page)
> + if (page) {
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> + }
> return 0;
> }
>
> @@ -336,12 +342,14 @@ static int gmap_alloc_table(struct gmap *gmap, unsigned long *table,
> static unsigned long __gmap_segment_gaddr(unsigned long *entry)
> {
> struct page *page;
> - unsigned long offset;
> + unsigned long offset, mask;
>
> offset = (unsigned long) entry / sizeof(unsigned long);
> offset = (offset & (PTRS_PER_PMD - 1)) * PMD_SIZE;
> - page = pmd_pgtable_page((pmd_t *) entry);
> - return page->index + offset;
> + mask = ~(PTRS_PER_PMD * sizeof(pmd_t) - 1);
> + page = virt_to_page((void *)((unsigned long) entry & mask));
> +
> + return page->_pt_s390_gaddr + offset;
> }
>
> /**
> @@ -1351,6 +1359,7 @@ static void gmap_unshadow_pgt(struct gmap *sg, unsigned long raddr)
> /* Free page table */
> page = phys_to_page(pgt);
> list_del(&page->lru);
> + page->_pt_s390_gaddr = 0;
> page_table_free_pgste(page);
> }
>
> @@ -1379,6 +1388,7 @@ static void __gmap_unshadow_sgt(struct gmap *sg, unsigned long raddr,
> /* Free page table */
> page = phys_to_page(pgt);
> list_del(&page->lru);
> + page->_pt_s390_gaddr = 0;
> page_table_free_pgste(page);
> }
> }
> @@ -1409,6 +1419,7 @@ static void gmap_unshadow_sgt(struct gmap *sg, unsigned long raddr)
> /* Free segment table */
> page = phys_to_page(sgt);
> list_del(&page->lru);
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> }
>
> @@ -1437,6 +1448,7 @@ static void __gmap_unshadow_r3t(struct gmap *sg, unsigned long raddr,
> /* Free segment table */
> page = phys_to_page(sgt);
> list_del(&page->lru);
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> }
> }
> @@ -1467,6 +1479,7 @@ static void gmap_unshadow_r3t(struct gmap *sg, unsigned long raddr)
> /* Free region 3 table */
> page = phys_to_page(r3t);
> list_del(&page->lru);
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> }
>
> @@ -1495,6 +1508,7 @@ static void __gmap_unshadow_r2t(struct gmap *sg, unsigned long raddr,
> /* Free region 3 table */
> page = phys_to_page(r3t);
> list_del(&page->lru);
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> }
> }
> @@ -1525,6 +1539,7 @@ static void gmap_unshadow_r2t(struct gmap *sg, unsigned long raddr)
> /* Free region 2 table */
> page = phys_to_page(r2t);
> list_del(&page->lru);
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> }
>
> @@ -1557,6 +1572,7 @@ static void __gmap_unshadow_r1t(struct gmap *sg, unsigned long raddr,
> /* Free region 2 table */
> page = phys_to_page(r2t);
> list_del(&page->lru);
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> }
> }
> @@ -1762,9 +1778,9 @@ int gmap_shadow_r2t(struct gmap *sg, unsigned long saddr, unsigned long r2t,
> page = alloc_pages(GFP_KERNEL_ACCOUNT, CRST_ALLOC_ORDER);
> if (!page)
> return -ENOMEM;
> - page->index = r2t & _REGION_ENTRY_ORIGIN;
> + page->_pt_s390_gaddr = r2t & _REGION_ENTRY_ORIGIN;
> if (fake)
> - page->index |= GMAP_SHADOW_FAKE_TABLE;
> + page->_pt_s390_gaddr |= GMAP_SHADOW_FAKE_TABLE;
> s_r2t = page_to_phys(page);
> /* Install shadow region second table */
> spin_lock(&sg->guest_table_lock);
> @@ -1814,6 +1830,7 @@ int gmap_shadow_r2t(struct gmap *sg, unsigned long saddr, unsigned long r2t,
> return rc;
> out_free:
> spin_unlock(&sg->guest_table_lock);
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> return rc;
> }
> @@ -1846,9 +1863,9 @@ int gmap_shadow_r3t(struct gmap *sg, unsigned long saddr, unsigned long r3t,
> page = alloc_pages(GFP_KERNEL_ACCOUNT, CRST_ALLOC_ORDER);
> if (!page)
> return -ENOMEM;
> - page->index = r3t & _REGION_ENTRY_ORIGIN;
> + page->_pt_s390_gaddr = r3t & _REGION_ENTRY_ORIGIN;
> if (fake)
> - page->index |= GMAP_SHADOW_FAKE_TABLE;
> + page->_pt_s390_gaddr |= GMAP_SHADOW_FAKE_TABLE;
> s_r3t = page_to_phys(page);
> /* Install shadow region second table */
> spin_lock(&sg->guest_table_lock);
> @@ -1898,6 +1915,7 @@ int gmap_shadow_r3t(struct gmap *sg, unsigned long saddr, unsigned long r3t,
> return rc;
> out_free:
> spin_unlock(&sg->guest_table_lock);
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> return rc;
> }
> @@ -1930,9 +1948,9 @@ int gmap_shadow_sgt(struct gmap *sg, unsigned long saddr, unsigned long sgt,
> page = alloc_pages(GFP_KERNEL_ACCOUNT, CRST_ALLOC_ORDER);
> if (!page)
> return -ENOMEM;
> - page->index = sgt & _REGION_ENTRY_ORIGIN;
> + page->_pt_s390_gaddr = sgt & _REGION_ENTRY_ORIGIN;
> if (fake)
> - page->index |= GMAP_SHADOW_FAKE_TABLE;
> + page->_pt_s390_gaddr |= GMAP_SHADOW_FAKE_TABLE;
> s_sgt = page_to_phys(page);
> /* Install shadow region second table */
> spin_lock(&sg->guest_table_lock);
> @@ -1982,6 +2000,7 @@ int gmap_shadow_sgt(struct gmap *sg, unsigned long saddr, unsigned long sgt,
> return rc;
> out_free:
> spin_unlock(&sg->guest_table_lock);
> + page->_pt_s390_gaddr = 0;
> __free_pages(page, CRST_ALLOC_ORDER);
> return rc;
> }
> @@ -2014,9 +2033,9 @@ int gmap_shadow_pgt_lookup(struct gmap *sg, unsigned long saddr,
> if (table && !(*table & _SEGMENT_ENTRY_INVALID)) {
> /* Shadow page tables are full pages (pte+pgste) */
> page = pfn_to_page(*table >> PAGE_SHIFT);
> - *pgt = page->index & ~GMAP_SHADOW_FAKE_TABLE;
> + *pgt = page->_pt_s390_gaddr & ~GMAP_SHADOW_FAKE_TABLE;
> *dat_protection = !!(*table & _SEGMENT_ENTRY_PROTECT);
> - *fake = !!(page->index & GMAP_SHADOW_FAKE_TABLE);
> + *fake = !!(page->_pt_s390_gaddr & GMAP_SHADOW_FAKE_TABLE);
> rc = 0;
> } else {
> rc = -EAGAIN;
> @@ -2054,9 +2073,9 @@ int gmap_shadow_pgt(struct gmap *sg, unsigned long saddr, unsigned long pgt,
> page = page_table_alloc_pgste(sg->mm);
> if (!page)
> return -ENOMEM;
> - page->index = pgt & _SEGMENT_ENTRY_ORIGIN;
> + page->_pt_s390_gaddr = pgt & _SEGMENT_ENTRY_ORIGIN;
> if (fake)
> - page->index |= GMAP_SHADOW_FAKE_TABLE;
> + page->_pt_s390_gaddr |= GMAP_SHADOW_FAKE_TABLE;
> s_pgt = page_to_phys(page);
> /* Install shadow page table */
> spin_lock(&sg->guest_table_lock);
> @@ -2101,6 +2120,7 @@ int gmap_shadow_pgt(struct gmap *sg, unsigned long saddr, unsigned long pgt,
> return rc;
> out_free:
> spin_unlock(&sg->guest_table_lock);
> + page->_pt_s390_gaddr = 0;
> page_table_free_pgste(page);
> return rc;
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 306a3d1a0fa6..6161fe1ae5b8 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -144,7 +144,7 @@ struct page {
> struct { /* Page table pages */
> unsigned long _pt_pad_1; /* compound_head */
> pgtable_t pmd_huge_pte; /* protected by page->ptl */
> - unsigned long _pt_pad_2; /* mapping */
> + unsigned long _pt_s390_gaddr; /* mapping */
> union {
> struct mm_struct *pt_mm; /* x86 pgds only */
> atomic_t pt_frag_refcount; /* powerpc */
> --
> 2.39.2
>
>

--
Sincerely yours,
Mike.