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[87.17.106.94]) by smtp.gmail.com with ESMTPSA id 10-20020a170906218a00b0072af2460cd6sm2875378eju.30.2022.08.19.15.31.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Aug 2022 15:31:33 -0700 (PDT) From: "Fabio M. De Francesco" To: Matthew Wilcox Cc: linux-fscrypt@vger.kernel.org, Eric Biggers , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] fs-verity: use kmap_local_page() instead of kmap() Date: Sat, 20 Aug 2022 00:31:31 +0200 Message-ID: <2255194.ElGaqSPkdT@opensuse> In-Reply-To: References: <20220818224010.43778-1-ebiggers@kernel.org> <44912540.fMDQidcC6G@opensuse> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On venerd=C3=AC 19 agosto 2022 20:29:31 CEST Matthew Wilcox wrote: > On Fri, Aug 19, 2022 at 09:50:37AM +0200, Fabio M. De Francesco wrote: > > On venerd=C3=AC 19 agosto 2022 00:40:10 CEST Eric Biggers wrote: > > > From: Eric Biggers > > >=20 > > > Convert the use of kmap() to its recommended replacement > > > kmap_local_page(). This avoids the overhead of doing a non-local > > > mapping, which is unnecessary in this case. > > >=20 > > > Signed-off-by: Eric Biggers > > > --- > > >=20 > > > fs/verity/read_metadata.c | 6 +++--- > > > 1 file changed, 3 insertions(+), 3 deletions(-) > >=20 > > It looks good to me... > >=20 > > > - virt =3D kmap(page); > > > + virt =3D kmap_local_page(page); > > >=20 > > > if (copy_to_user(buf, virt + offs_in_page, bytes_to_copy)) > >=20 > > { > >=20 > > > - kunmap(page); > > > + kunmap_local(virt); > > >=20 > > > put_page(page); > > > err =3D -EFAULT; > > > break; > > > =09 > > > } > > >=20 > > > - kunmap(page); > > > + kunmap_local(virt); >=20 > Is this a common pattern? eg do we want something like: >=20 > static inline int copy_user_page(void __user *dst, struct page *page, > size_t offset, size_t len) > { > char *src =3D kmap_local_page(page) + offset; > int err =3D 0; >=20 > VM_BUG_ON(offset + len > PAGE_SIZE); > if (copy_to_user(dst, src, len)) > err =3D -EFAULT; >=20 > kunmap_local(src); > return err; > } >=20 > in highmem.h? Not sure that it is much common... Can the following command provide any insight? opensuse:/usr/src/git/kernels/linux> grep -rn copy_to_user -B7 . --exclude- dir\=3DDocumentation | grep kmap =2E/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c-2306- ptr =3D=20 kmap_local_page(p); =2E/drivers/gpu/drm/i915/i915_gem.c-215- vaddr =3D kmap_local_page(page); =2E/drivers/gpu/drm/radeon/radeon_ttm.c-872- ptr =3D=20 kmap(page); =2E/drivers/vfio/pci/mlx5/main.c-182- from_buff =3D=20 kmap_local_page(page); =2E/arch/parisc/kernel/cache.c-580- kto =3D kmap_local_page(to); =2E/mm/memory.c-5474- maddr =3D kmap(page); =2E/fs/verity/read_metadata.c-56- virt =3D kmap(page); =2E/fs/aio.c-1252- ev =3D kmap_local_page(page); =2E/fs/exec.c-883- char *src =3D kmap_local_page(bprm->page[= index])=20 + offset; If this command is good to provide any hint, it suggests that having=20 copy_to_user() in highmem.h is not probably worth. Thanks, =46abio=20