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Fri, 21 Jul 2023 12:58:38 +0200 (CEST) Message-ID: <20230721105744.571094000@infradead.org> User-Agent: quilt/0.66 Date: Fri, 21 Jul 2023 12:22:50 +0200 From: Peter Zijlstra To: tglx@linutronix.de, axboe@kernel.dk Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, dvhart@infradead.org, dave@stgolabs.net, andrealmeid@igalia.com, Andrew Morton , urezki@gmail.com, hch@infradead.org, lstoakes@gmail.com, Arnd Bergmann , linux-api@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, malteskarupke@web.de Subject: [PATCH v1 13/14] futex: Enable FUTEX2_{8,16} References: <20230721102237.268073801@infradead.org> MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 15FFB140009 X-Stat-Signature: ycas7kj1bo1erfi5nazarbupbeackq4s X-HE-Tag: 1689937133-345454 X-HE-Meta: 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 /uMzX0O1 8swfDyRGOvyBw7ZWR74xSrksbMvKUiKcISMmzToKiVYPOsEx9RK4gNbib6LXS+yKNhc1LRceYYK9nh2NqHzS/tCdAnk78yZZwHs/hTmNwoEEk7kBTmDyfhcvi9/Zpe/Pedny1mB1j0/EuBocdBPEFPbcZKLzLyHCE9UEj1VZXP9Y3JwOexxXQ104Mxl5RmsYs79X0IVQi8hq49EkSRkIpQu9W6Lb+alzQ+HK9bIVEHetBFJ20aEDgEAs0NquNYmD1PEu4cKQhQVYbRAwrZEgimiD3nKSqJA0DtTUkMcBC3FQ7YkEh/EEAdoJLj4cT1bzJ6/lj X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: When futexes are no longer u32 aligned, the lower offset bits are no longer available to put type info in. However, since offset is the offset within a page, there are plenty bits available on the top end. After that, pass flags into futex_get_value_locked() for WAIT and disallow FUTEX2_64 instead of mandating FUTEX2_32. Signed-off-by: Peter Zijlstra (Intel) --- include/linux/futex.h | 11 ++++++----- kernel/futex/core.c | 9 +++++++++ kernel/futex/futex.h | 4 ++-- kernel/futex/waitwake.c | 5 +++-- 4 files changed, 20 insertions(+), 9 deletions(-) --- a/include/linux/futex.h +++ b/include/linux/futex.h @@ -16,18 +16,19 @@ struct task_struct; * The key type depends on whether it's a shared or private mapping. * Don't rearrange members without looking at hash_futex(). * - * offset is aligned to a multiple of sizeof(u32) (== 4) by definition. - * We use the two low order bits of offset to tell what is the kind of key : + * offset is the position within a page and is in the range [0, PAGE_SIZE). + * The high bits of the offset indicate what kind of key this is: * 00 : Private process futex (PTHREAD_PROCESS_PRIVATE) * (no reference on an inode or mm) * 01 : Shared futex (PTHREAD_PROCESS_SHARED) * mapped on a file (reference on the underlying inode) * 10 : Shared futex (PTHREAD_PROCESS_SHARED) * (but private mapping on an mm, and reference taken on it) -*/ + */ -#define FUT_OFF_INODE 1 /* We set bit 0 if key has a reference on inode */ -#define FUT_OFF_MMSHARED 2 /* We set bit 1 if key has a reference on mm */ +#define FUT_OFF_INODE (PAGE_SIZE << 0) +#define FUT_OFF_MMSHARED (PAGE_SIZE << 1) +#define FUT_OFF_SIZE (PAGE_SIZE << 2) union futex_key { struct { --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -308,6 +308,15 @@ int get_futex_key(void __user *uaddr, un } /* + * Encode the futex size in the offset. This makes cross-size + * wake-wait fail -- see futex_match(). + * + * NOTE that cross-size wake-wait is fundamentally broken wrt + * FLAGS_NUMA but could possibly work for !NUMA. + */ + key->both.offset |= FUT_OFF_SIZE * (flags & FLAGS_SIZE_MASK); + + /* * PROCESS_PRIVATE futexes are fast. * As the mm cannot disappear under us and the 'key' only needs * virtual address, we dont even have to find the underlying vma. --- a/kernel/futex/futex.h +++ b/kernel/futex/futex.h @@ -79,8 +79,8 @@ static inline bool futex_flags_valid(uns return false; } - /* Only 32bit futexes are implemented -- for now */ - if ((flags & FLAGS_SIZE_MASK) != FLAGS_SIZE_32) + /* 64bit futexes aren't implemented -- yet */ + if ((flags & FLAGS_SIZE_MASK) == FLAGS_SIZE_64) return false; /* --- a/kernel/futex/waitwake.c +++ b/kernel/futex/waitwake.c @@ -434,11 +434,12 @@ static int futex_wait_multiple_setup(str for (i = 0; i < count; i++) { u32 __user *uaddr = (u32 __user *)(unsigned long)vs[i].w.uaddr; + unsigned int flags = vs[i].w.flags; struct futex_q *q = &vs[i].q; u32 val = vs[i].w.val; hb = futex_q_lock(q); - ret = futex_get_value_locked(&uval, uaddr, FLAGS_SIZE_32); + ret = futex_get_value_locked(&uval, uaddr, flags); if (!ret && uval == val) { /* @@ -606,7 +607,7 @@ int futex_wait_setup(u32 __user *uaddr, retry_private: *hb = futex_q_lock(q); - ret = futex_get_value_locked(&uval, uaddr, FLAGS_SIZE_32); + ret = futex_get_value_locked(&uval, uaddr, flags); if (ret) { futex_q_unlock(*hb);