From patchwork Mon Apr 15 07:13:56 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alice Ryhl X-Patchwork-Id: 13629530 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4B517C4345F for ; Mon, 15 Apr 2024 07:14:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D28FB6B0099; Mon, 15 Apr 2024 03:14:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CD47D6B009A; Mon, 15 Apr 2024 03:14:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B28B66B009B; Mon, 15 Apr 2024 03:14:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 892856B0099 for ; Mon, 15 Apr 2024 03:14:30 -0400 (EDT) Received: from smtpin21.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 5B648120478 for ; Mon, 15 Apr 2024 07:14:30 +0000 (UTC) X-FDA: 82010903100.21.4B1DE22 Received: from mail-lf1-f74.google.com (mail-lf1-f74.google.com [209.85.167.74]) by imf30.hostedemail.com (Postfix) with ESMTP id 5850D80011 for ; Mon, 15 Apr 2024 07:14:28 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=3PwfzN6j; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf30.hostedemail.com: domain of 30tMcZgkKCCUBMJDFSZIMHPPHMF.DPNMJOVY-NNLWBDL.PSH@flex--aliceryhl.bounces.google.com designates 209.85.167.74 as permitted sender) smtp.mailfrom=30tMcZgkKCCUBMJDFSZIMHPPHMF.DPNMJOVY-NNLWBDL.PSH@flex--aliceryhl.bounces.google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1713165268; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=dQnBVtrhJpUgOHcm+nS3apY4eRmi29T+h46zYZ5XaoI=; b=78VEa3qNLxTj4ubRUuUw7rM08BqQs35OlB7/5CfHt+/n+xfnJa8ot5pEKoaZnFFw+D09V0 xZt4w5mtHreKCbgJwMH9PRQ0K2vald9z+PapQWtqHzFAu466jyJZsyX9/eST9TImSNM4dC 0uTuJC53C3LC5/u7m4eEbDjTFAmEI1c= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=3PwfzN6j; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf30.hostedemail.com: domain of 30tMcZgkKCCUBMJDFSZIMHPPHMF.DPNMJOVY-NNLWBDL.PSH@flex--aliceryhl.bounces.google.com designates 209.85.167.74 as permitted sender) smtp.mailfrom=30tMcZgkKCCUBMJDFSZIMHPPHMF.DPNMJOVY-NNLWBDL.PSH@flex--aliceryhl.bounces.google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1713165268; a=rsa-sha256; cv=none; b=WgT7ZB+z4/xZo5BUiuk9X1aZ4kgWrIWzgM8nyaxFla4tZ1JKIyVm831gmPCxfQ/QJDt9c5 S6vnvZkD4lRH0Bir47KSb3aMkAe+UCRfneG76qhCVcUTjBWzIeqqpb9MkSNlIjSk0ofX6g xWxbiFdYA7xt9mvgMnAZRHMCmwKoqyw= Received: by mail-lf1-f74.google.com with SMTP id 2adb3069b0e04-516d46e1bafso1385321e87.2 for ; Mon, 15 Apr 2024 00:14:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1713165266; x=1713770066; darn=kvack.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=dQnBVtrhJpUgOHcm+nS3apY4eRmi29T+h46zYZ5XaoI=; b=3PwfzN6jdPelYK0z3nM0Hpd8OD+qRUyZONDzqXdhwsAR+beKiAy3RY0YWNivAtKy8H W4vmOShbGZeyTb8viI1dfDJKqicjDMpS/13n1pMvJN+k3N0zuTFbO9CBa5L4ZKyLM0d/ 4JTx2yboQ+XrO313dWPde/MxgW5fmjGQ1ljoLQFMzoj1JYquIKPBnnK7DskEptoNzojH GnilU7ZgGVrSEaEb0tMckJX2c1Ym1c3iglzTtbMarru2BFBC9KRzqFPX4CmN1cDI4HjK pzAfiolaHKp78qLzCvbC8zTTV476SpiAJkfDh6uxOyM2pkm0QTx4lbj8nF3e2MCU4W2d gkTA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1713165266; x=1713770066; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=dQnBVtrhJpUgOHcm+nS3apY4eRmi29T+h46zYZ5XaoI=; b=mb7YGH5k04ZZRod7jMctOGEqqPB1S8P7xRaopaNrx3Uaf5nyUA0eXJUgIo9y/WAEGh zZ4e0b7MUyk73J9dTv+L+B28eoCWRROPJWEedR05qyo4950b7sIxzBErCFMhg1KbEjia jceUVESHRA/HHEgtpFS2SSMWJT3l46Sk8OeFemuK09VxfceNh1aQTaD1EzOHwRske1Ar P5GURGLUWQA5uOOJEHwGY7sdWajx/V+xTYDXOprv4FWabE892RovkoqLL/ag8vuh8sxO jWOFVBDLUBzuiiurTROjd9V1S1wPkWZReLWe6ZKCPe/YuRx5MWc0G38RxZ5gslffxKvy wDiw== X-Forwarded-Encrypted: i=1; AJvYcCU4VbvaizMOQw+oyU/6UyZrIz+LUWSZHw1ffE+hwuOrFs/qFeRFy9e1JF3q00C1SwUZhU1Oa50Qivi1HR7fUYaKmug= X-Gm-Message-State: AOJu0YzNF9I6z0Mbph2U7ndtoL0+SbZtP0KH3lRq7IKj960ANpvZhNWE S105xxrA60zeq3QdshwloYldJJB1KEG+O3yw6yWUkdr1C9Wq3gUs2FCqgA589gdvP3KySHomJqo 2o8Zs0nxpXtTNAg== X-Google-Smtp-Source: AGHT+IGj4s5XcuUlnHXAqbbbB0vr64kBb3ewtMkKntnALdO/9Wx+FqLH+bIRcaQ7/jFxocSOccqLI8Do0Wig5+w= X-Received: from aliceryhl2.c.googlers.com ([fda3:e722:ac3:cc00:68:949d:c0a8:572]) (user=aliceryhl job=sendgmr) by 2002:a05:6512:2c8c:b0:518:c9cc:f169 with SMTP id dw12-20020a0565122c8c00b00518c9ccf169mr2703lfb.9.1713165266687; Mon, 15 Apr 2024 00:14:26 -0700 (PDT) Date: Mon, 15 Apr 2024 07:13:56 +0000 In-Reply-To: <20240415-alice-mm-v5-0-6f55e4d8ef51@google.com> Mime-Version: 1.0 References: <20240415-alice-mm-v5-0-6f55e4d8ef51@google.com> X-Developer-Key: i=aliceryhl@google.com; a=openpgp; fpr=49F6C1FAA74960F43A5B86A1EE7A392FDE96209F X-Developer-Signature: v=1; a=openpgp-sha256; l=15423; i=aliceryhl@google.com; h=from:subject:message-id; bh=8G034x9QLKwhszhfSOV4sRo/vOkKD0+Y6xZHnepJVr8=; b=owEBbQKS/ZANAwAKAQRYvu5YxjlGAcsmYgBmHNPDsrivyGBAl1qNxYjiDLbuOvR9BBC9GJHRV SrTL5tsTTKJAjMEAAEKAB0WIQSDkqKUTWQHCvFIvbIEWL7uWMY5RgUCZhzTwwAKCRAEWL7uWMY5 RgbyEAC8Hby5pqtDLGHCfFHFUfA2ZVFgjQRHb7wotVVMNsB+JBI+okpEmkq1hVQ9IKfIqJhp3M4 1x4USMZMPWhgRqW5axodDBKLmyTHx25xMXZzs30QZWBlAzdQoTDCd7/kg2ifWL65XKzq/zwCa23 URd08TKx9DxT4rrtzz351hEQiGHMqHAdv90PkVjpi2WciRbuJhezN1chFIQBfHaA3wjc9wOkCvP TnUiM0yfI8FtWa45XFjHzIFXfb8Ol+m+HlQaBRs5pLrnceju1Fx6gK3yTLZcEE4vYBDaN60EsZJ IgPy9KcygbA9eD+qC/62oP+6+fjRUcWsaJWbxXiW+4j143NnHBMVuABzAJjv2plFjG9cLXF9H+L 7o7TJv8jRtFy9pJ3PMDk1sIv8P5az9x1ZLvopcCb42By5FyIOTVONzU/lP+7VN/rNGaRRm3dyij 0p9KtomDU9I4AvMG+RVOKpcGCEr4vraHoXjKqvu+VMwIj8q9ZCkdP+2HHZOHKWBnoWeZYItXExR mk195VQK4ICe14p7mz9yVNkC6CJ9ddk0OU2HXugUrBS3Rvr9td5Vf+mtdRua8sptmOq4/nta/uC NyXMM2Kwvtz76AFraOwujbgfAsmlAYAcIVsoAYy9n5oI6mef2PQIQ15or4w89JHnLrBMygqRoCP nSz+HTDGgKd+Ndw== X-Mailer: b4 0.13-dev-26615 Message-ID: <20240415-alice-mm-v5-4-6f55e4d8ef51@google.com> Subject: [PATCH v5 4/4] rust: add abstraction for `struct page` From: Alice Ryhl To: Miguel Ojeda , Matthew Wilcox , Al Viro , Andrew Morton , Kees Cook Cc: Alex Gaynor , Wedson Almeida Filho , Boqun Feng , Gary Guo , " =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= " , Benno Lossin , Andreas Hindborg , Greg Kroah-Hartman , " =?utf-8?q?Arve_Hj=C3=B8?= =?utf-8?q?nnev=C3=A5g?= " , Todd Kjos , Martijn Coenen , Joel Fernandes , Carlos Llamas , Suren Baghdasaryan , Arnd Bergmann , linux-mm@kvack.org, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, Alice Ryhl , Christian Brauner X-Rspamd-Queue-Id: 5850D80011 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: uz3y7kfjkw3iwwfj9naeto1uyeo98kms X-HE-Tag: 1713165268-342097 X-HE-Meta: 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 +ua8vyYU 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 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: List-Subscribe: List-Unsubscribe: Adds a new struct called `Page` that wraps a pointer to `struct page`. This struct is assumed to hold ownership over the page, so that Rust code can allocate and manage pages directly. The page type has various methods for reading and writing into the page. These methods will temporarily map the page to allow the operation. All of these methods use a helper that takes an offset and length, performs bounds checks, and returns a pointer to the given offset in the page. This patch only adds support for pages of order zero, as that is all Rust Binder needs. However, it is written to make it easy to add support for higher-order pages in the future. To do that, you would add a const generic parameter to `Page` that specifies the order. Most of the methods do not need to be adjusted, as the logic for dealing with mapping multiple pages at once can be isolated to just the `with_pointer_into_page` method. Rust Binder needs to manage pages directly as that is how transactions are delivered: Each process has an mmap'd region for incoming transactions. When an incoming transaction arrives, the Binder driver will choose a region in the mmap, allocate and map the relevant pages manually, and copy the incoming transaction directly into the page. This architecture allows the driver to copy transactions directly from the address space of one process to another, without an intermediate copy to a kernel buffer. This code is based on Wedson's page abstractions from the old rust branch, but it has been modified by Alice by removing the incomplete support for higher-order pages, by introducing the `with_*` helpers to consolidate the bounds checking logic into a single place, and by introducing gfp flags. Co-developed-by: Wedson Almeida Filho Signed-off-by: Wedson Almeida Filho Signed-off-by: Alice Ryhl Reviewed-by: Andreas Hindborg Reviewed-by: Benno Lossin Reviewed-by: Trevor Gross --- rust/bindings/bindings_helper.h | 2 + rust/helpers.c | 20 ++++ rust/kernel/lib.rs | 1 + rust/kernel/page.rs | 240 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 263 insertions(+) diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index 65b98831b975..da1e97871419 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -20,5 +20,7 @@ /* `bindgen` gets confused at certain things. */ const size_t RUST_CONST_HELPER_ARCH_SLAB_MINALIGN = ARCH_SLAB_MINALIGN; +const size_t RUST_CONST_HELPER_PAGE_SIZE = PAGE_SIZE; const gfp_t RUST_CONST_HELPER_GFP_KERNEL = GFP_KERNEL; const gfp_t RUST_CONST_HELPER___GFP_ZERO = __GFP_ZERO; +const gfp_t RUST_CONST_HELPER___GFP_HIGHMEM = ___GFP_HIGHMEM; diff --git a/rust/helpers.c b/rust/helpers.c index 312b6fcb49d5..72361003ba91 100644 --- a/rust/helpers.c +++ b/rust/helpers.c @@ -25,6 +25,8 @@ #include #include #include +#include +#include #include #include #include @@ -93,6 +95,24 @@ int rust_helper_signal_pending(struct task_struct *t) } EXPORT_SYMBOL_GPL(rust_helper_signal_pending); +struct page *rust_helper_alloc_pages(gfp_t gfp_mask, unsigned int order) +{ + return alloc_pages(gfp_mask, order); +} +EXPORT_SYMBOL_GPL(rust_helper_alloc_pages); + +void *rust_helper_kmap_local_page(struct page *page) +{ + return kmap_local_page(page); +} +EXPORT_SYMBOL_GPL(rust_helper_kmap_local_page); + +void rust_helper_kunmap_local(const void *addr) +{ + kunmap_local(addr); +} +EXPORT_SYMBOL_GPL(rust_helper_kunmap_local); + refcount_t rust_helper_REFCOUNT_INIT(int n) { return (refcount_t)REFCOUNT_INIT(n); diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 37f84223b83f..667fc67fa24f 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -39,6 +39,7 @@ pub mod kunit; #[cfg(CONFIG_NET)] pub mod net; +pub mod page; pub mod prelude; pub mod print; mod static_assert; diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs new file mode 100644 index 000000000000..f7f8870ddb66 --- /dev/null +++ b/rust/kernel/page.rs @@ -0,0 +1,240 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Kernel page allocation and management. + +use crate::{bindings, error::code::*, error::Result, uaccess::UserSliceReader}; +use core::{ + alloc::AllocError, + ptr::{self, NonNull}, +}; + +/// A bitwise shift for the page size. +pub const PAGE_SHIFT: usize = bindings::PAGE_SHIFT as usize; + +/// The number of bytes in a page. +pub const PAGE_SIZE: usize = bindings::PAGE_SIZE; + +/// A bitmask that gives the page containing a given address. +pub const PAGE_MASK: usize = !(PAGE_SIZE - 1); + +/// Flags for the "get free page" function that underlies all memory allocations. +pub mod flags { + /// gfp flags. + #[allow(non_camel_case_types)] + pub type gfp_t = bindings::gfp_t; + + /// `GFP_KERNEL` is typical for kernel-internal allocations. The caller requires `ZONE_NORMAL` + /// or a lower zone for direct access but can direct reclaim. + pub const GFP_KERNEL: gfp_t = bindings::GFP_KERNEL; + /// `GFP_ZERO` returns a zeroed page on success. + pub const __GFP_ZERO: gfp_t = bindings::__GFP_ZERO; + /// `GFP_HIGHMEM` indicates that the allocated memory may be located in high memory. + pub const __GFP_HIGHMEM: gfp_t = bindings::__GFP_HIGHMEM; +} + +/// A pointer to a page that owns the page allocation. +/// +/// # Invariants +/// +/// The pointer is valid, and has ownership over the page. +pub struct Page { + page: NonNull, +} + +// SAFETY: Pages have no logic that relies on them staying on a given thread, so moving them across +// threads is safe. +unsafe impl Send for Page {} + +// SAFETY: Pages have no logic that relies on them not being accessed concurrently, so accessing +// them concurrently is safe. +unsafe impl Sync for Page {} + +impl Page { + /// Allocates a new page. + pub fn alloc_page(gfp_flags: flags::gfp_t) -> Result { + // SAFETY: Depending on the value of `gfp_flags`, this call may sleep. Other than that, it + // is always safe to call this method. + let page = unsafe { bindings::alloc_pages(gfp_flags, 0) }; + let page = NonNull::new(page).ok_or(AllocError)?; + // INVARIANT: We just successfully allocated a page, so we now have ownership of the newly + // allocated page. We transfer that ownership to the new `Page` object. + Ok(Self { page }) + } + + /// Returns a raw pointer to the page. + pub fn as_ptr(&self) -> *mut bindings::page { + self.page.as_ptr() + } + + /// Runs a piece of code with this page mapped to an address. + /// + /// The page is unmapped when this call returns. + /// + /// # Using the raw pointer + /// + /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for + /// `PAGE_SIZE` bytes and for the duration in which the closure is called. The pointer might + /// only be mapped on the current thread, and when that is the case, dereferencing it on other + /// threads is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't + /// cause data races, the memory may be uninitialized, and so on. + /// + /// If multiple threads map the same page at the same time, then they may reference with + /// different addresses. However, even if the addresses are different, the underlying memory is + /// still the same for these purposes (e.g., it's still a data race if they both write to the + /// same underlying byte at the same time). + fn with_page_mapped(&self, f: impl FnOnce(*mut u8) -> T) -> T { + // SAFETY: `page` is valid due to the type invariants on `Page`. + let mapped_addr = unsafe { bindings::kmap_local_page(self.as_ptr()) }; + + let res = f(mapped_addr.cast()); + + // This unmaps the page mapped above. + // + // SAFETY: Since this API takes the user code as a closure, it can only be used in a manner + // where the pages are unmapped in reverse order. This is as required by `kunmap_local`. + // + // In other words, if this call to `kunmap_local` happens when a different page should be + // unmapped first, then there must necessarily be a call to `kmap_local_page` other than the + // call just above in `with_page_mapped` that made that possible. In this case, it is the + // unsafe block that wraps that other call that is incorrect. + unsafe { bindings::kunmap_local(mapped_addr) }; + + res + } + + /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking. + /// + /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the + /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on + /// this task, as this method uses a local mapping. + /// + /// If `off` and `len` refers to a region outside of this page, then this method returns + /// `EINVAL` and does not call `f`. + /// + /// # Using the raw pointer + /// + /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for + /// `len` bytes and for the duration in which the closure is called. The pointer might only be + /// mapped on the current thread, and when that is the case, dereferencing it on other threads + /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause + /// data races, the memory may be uninitialized, and so on. + /// + /// If multiple threads map the same page at the same time, then they may reference with + /// different addresses. However, even if the addresses are different, the underlying memory is + /// still the same for these purposes (e.g., it's still a data race if they both write to the + /// same underlying byte at the same time). + fn with_pointer_into_page( + &self, + off: usize, + len: usize, + f: impl FnOnce(*mut u8) -> Result, + ) -> Result { + let bounds_ok = off <= PAGE_SIZE && len <= PAGE_SIZE && (off + len) <= PAGE_SIZE; + + if bounds_ok { + self.with_page_mapped(move |page_addr| { + // SAFETY: The `off` integer is at most `PAGE_SIZE`, so this pointer offset will + // result in a pointer that is in bounds or one off the end of the page. + f(unsafe { page_addr.add(off) }) + }) + } else { + Err(EINVAL) + } + } + + /// Maps the page and reads from it into the given buffer. + /// + /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes + /// outside ot the page, then this call returns `EINVAL`. + /// + /// # Safety + /// + /// * Callers must ensure that `dst` is valid for writing `len` bytes. + /// * Callers must ensure that this call does not race with a write to the same page that + /// overlaps with this read. + pub unsafe fn read_raw(&self, dst: *mut u8, offset: usize, len: usize) -> Result { + self.with_pointer_into_page(offset, len, move |src| { + // SAFETY: If `with_pointer_into_page` calls into this closure, then + // it has performed a bounds check and guarantees that `src` is + // valid for `len` bytes. + // + // There caller guarantees that there is no data race. + unsafe { ptr::copy_nonoverlapping(src, dst, len) }; + Ok(()) + }) + } + + /// Maps the page and writes into it from the given buffer. + /// + /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes + /// outside ot the page, then this call returns `EINVAL`. + /// + /// # Safety + /// + /// * Callers must ensure that `src` is valid for reading `len` bytes. + /// * Callers must ensure that this call does not race with a read or write to the same page + /// that overlaps with this write. + pub unsafe fn write_raw(&self, src: *const u8, offset: usize, len: usize) -> Result { + self.with_pointer_into_page(offset, len, move |dst| { + // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a + // bounds check and guarantees that `dst` is valid for `len` bytes. + // + // There caller guarantees that there is no data race. + unsafe { ptr::copy_nonoverlapping(src, dst, len) }; + Ok(()) + }) + } + + /// Maps the page and zeroes the given slice. + /// + /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes + /// outside ot the page, then this call returns `EINVAL`. + /// + /// # Safety + /// + /// Callers must ensure that this call does not race with a read or write to the same page that + /// overlaps with this write. + pub unsafe fn fill_zero(&self, offset: usize, len: usize) -> Result { + self.with_pointer_into_page(offset, len, move |dst| { + // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a + // bounds check and guarantees that `dst` is valid for `len` bytes. + // + // There caller guarantees that there is no data race. + unsafe { ptr::write_bytes(dst, 0u8, len) }; + Ok(()) + }) + } + + /// Copies data from userspace into this page. + /// + /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes + /// outside ot the page, then this call returns `EINVAL`. + /// + /// Like the other `UserSliceReader` methods, data races are allowed on the userspace address. + /// However, they are not allowed on the page you are copying into. + /// + /// # Safety + /// + /// Callers must ensure that this call does not race with a read or write to the same page that + /// overlaps with this write. + pub unsafe fn copy_from_user_slice( + &self, + reader: &mut UserSliceReader, + offset: usize, + len: usize, + ) -> Result { + self.with_pointer_into_page(offset, len, move |dst| { + // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a + // bounds check and guarantees that `dst` is valid for `len` bytes. Furthermore, we have + // exclusive access to the slice since the caller guarantees that there are no races. + reader.read_raw(unsafe { core::slice::from_raw_parts_mut(dst.cast(), len) }) + }) + } +} + +impl Drop for Page { + fn drop(&mut self) { + // SAFETY: By the type invariants, we have ownership of the page and can free it. + unsafe { bindings::__free_pages(self.page.as_ptr(), 0) }; + } +}