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Message-ID: <Z5uCFtyaDpcbHRoF@phenom.ffwll.local>
Date: Thu, 30 Jan 2025 14:43:50 +0100
From: Simona Vetter <simona.vetter@...ll.ch>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
dri-devel@...ts.freedesktop.org, linux-mm@...ck.org,
nouveau@...ts.freedesktop.org,
Andrew Morton <akpm@...ux-foundation.org>,
Jérôme Glisse <jglisse@...hat.com>,
Jonathan Corbet <corbet@....net>, Alex Shi <alexs@...nel.org>,
Yanteng Si <si.yanteng@...ux.dev>,
Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>,
Danilo Krummrich <dakr@...nel.org>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Peter Xu <peterx@...hat.com>, Alistair Popple <apopple@...dia.com>,
Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v1 06/12] mm: use single SWP_DEVICE_EXCLUSIVE entry type
On Wed, Jan 29, 2025 at 12:54:04PM +0100, David Hildenbrand wrote:
> There is no need for the distinction anymore; let's merge the readable
> and writable device-exclusive entries into a single device-exclusive
> entry type.
>
> Signed-off-by: David Hildenbrand <david@...hat.com>
Yeah I really don't think there's a need to track that on the cpu ptes.
Device should have write/dirty bits (which nouveau really should forward)
or defensively assume the page is always dirtied when clearing a pte.
Plus the entire point of device exclusive access is to support device
atomics, so in practice it's always a write access that dirties anyway.
Acked-by: Simona Vetter <simona.vetter@...ll.ch>
> ---
> include/linux/swap.h | 7 +++----
> include/linux/swapops.h | 27 ++++-----------------------
> mm/mprotect.c | 8 --------
> mm/page_table_check.c | 5 ++---
> mm/rmap.c | 2 +-
> 5 files changed, 10 insertions(+), 39 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 91b30701274e..9a48e79a0a52 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -74,14 +74,13 @@ static inline int current_is_kswapd(void)
> * to a special SWP_DEVICE_{READ|WRITE} entry.
> *
> * When a page is mapped by the device for exclusive access we set the CPU page
> - * table entries to special SWP_DEVICE_EXCLUSIVE_* entries.
> + * table entries to a special SWP_DEVICE_EXCLUSIVE entry.
> */
> #ifdef CONFIG_DEVICE_PRIVATE
> -#define SWP_DEVICE_NUM 4
> +#define SWP_DEVICE_NUM 3
> #define SWP_DEVICE_WRITE (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM)
> #define SWP_DEVICE_READ (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+1)
> -#define SWP_DEVICE_EXCLUSIVE_WRITE (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+2)
> -#define SWP_DEVICE_EXCLUSIVE_READ (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+3)
> +#define SWP_DEVICE_EXCLUSIVE (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+2)
> #else
> #define SWP_DEVICE_NUM 0
> #endif
> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> index 96f26e29fefe..64ea151a7ae3 100644
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -186,26 +186,16 @@ static inline bool is_writable_device_private_entry(swp_entry_t entry)
> return unlikely(swp_type(entry) == SWP_DEVICE_WRITE);
> }
>
> -static inline swp_entry_t make_readable_device_exclusive_entry(pgoff_t offset)
> +static inline swp_entry_t make_device_exclusive_entry(pgoff_t offset)
> {
> - return swp_entry(SWP_DEVICE_EXCLUSIVE_READ, offset);
> -}
> -
> -static inline swp_entry_t make_writable_device_exclusive_entry(pgoff_t offset)
> -{
> - return swp_entry(SWP_DEVICE_EXCLUSIVE_WRITE, offset);
> + return swp_entry(SWP_DEVICE_EXCLUSIVE, offset);
> }
>
> static inline bool is_device_exclusive_entry(swp_entry_t entry)
> {
> - return swp_type(entry) == SWP_DEVICE_EXCLUSIVE_READ ||
> - swp_type(entry) == SWP_DEVICE_EXCLUSIVE_WRITE;
> + return swp_type(entry) == SWP_DEVICE_EXCLUSIVE;
> }
>
> -static inline bool is_writable_device_exclusive_entry(swp_entry_t entry)
> -{
> - return unlikely(swp_type(entry) == SWP_DEVICE_EXCLUSIVE_WRITE);
> -}
> #else /* CONFIG_DEVICE_PRIVATE */
> static inline swp_entry_t make_readable_device_private_entry(pgoff_t offset)
> {
> @@ -227,12 +217,7 @@ static inline bool is_writable_device_private_entry(swp_entry_t entry)
> return false;
> }
>
> -static inline swp_entry_t make_readable_device_exclusive_entry(pgoff_t offset)
> -{
> - return swp_entry(0, 0);
> -}
> -
> -static inline swp_entry_t make_writable_device_exclusive_entry(pgoff_t offset)
> +static inline swp_entry_t make_device_exclusive_entry(pgoff_t offset)
> {
> return swp_entry(0, 0);
> }
> @@ -242,10 +227,6 @@ static inline bool is_device_exclusive_entry(swp_entry_t entry)
> return false;
> }
>
> -static inline bool is_writable_device_exclusive_entry(swp_entry_t entry)
> -{
> - return false;
> -}
> #endif /* CONFIG_DEVICE_PRIVATE */
>
> #ifdef CONFIG_MIGRATION
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 516b1d847e2c..9cb6ab7c4048 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -225,14 +225,6 @@ static long change_pte_range(struct mmu_gather *tlb,
> newpte = swp_entry_to_pte(entry);
> if (pte_swp_uffd_wp(oldpte))
> newpte = pte_swp_mkuffd_wp(newpte);
> - } else if (is_writable_device_exclusive_entry(entry)) {
> - entry = make_readable_device_exclusive_entry(
> - swp_offset(entry));
> - newpte = swp_entry_to_pte(entry);
> - if (pte_swp_soft_dirty(oldpte))
> - newpte = pte_swp_mksoft_dirty(newpte);
> - if (pte_swp_uffd_wp(oldpte))
> - newpte = pte_swp_mkuffd_wp(newpte);
> } else if (is_pte_marker_entry(entry)) {
> /*
> * Ignore error swap entries unconditionally,
> diff --git a/mm/page_table_check.c b/mm/page_table_check.c
> index 509c6ef8de40..c2b3600429a0 100644
> --- a/mm/page_table_check.c
> +++ b/mm/page_table_check.c
> @@ -196,9 +196,8 @@ EXPORT_SYMBOL(__page_table_check_pud_clear);
> /* Whether the swap entry cached writable information */
> static inline bool swap_cached_writable(swp_entry_t entry)
> {
> - return is_writable_device_exclusive_entry(entry) ||
> - is_writable_device_private_entry(entry) ||
> - is_writable_migration_entry(entry);
> + return is_writable_device_private_entry(entry) ||
> + is_writable_migration_entry(entry);
> }
>
> static inline void page_table_check_pte_flags(pte_t pte)
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 49ffac6d27f8..65d9bbea16d0 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -2470,7 +2470,7 @@ struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr,
> * do_swap_page() will trigger the conversion back while holding the
> * folio lock.
> */
> - entry = make_writable_device_exclusive_entry(page_to_pfn(page));
> + entry = make_device_exclusive_entry(page_to_pfn(page));
> swp_pte = swp_entry_to_pte(entry);
> if (pte_soft_dirty(fw.pte))
> swp_pte = pte_swp_mksoft_dirty(swp_pte);
> --
> 2.48.1
>
--
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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