linux-kernel - [PATCH] fs: Replace kmap{,_atomic}() with kmap_local

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Date:   Thu, 30 Jun 2022 18:35:27 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Benjamin LaHaise <bcrl@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Chuck Lever <chuck.lever@...cle.com>,
        Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, nvdimm@...ts.linux.dev,
        io-uring@...r.kernel.org, linux-riscv@...ts.infradead.org,
        llvm@...ts.linux.dev
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Ira Weiny <ira.weiny@...el.com>
Subject: [PATCH] fs: Replace kmap{,_atomic}() with kmap_local_page()

The use of kmap() and kmap_atomic() are being deprecated in favor of
kmap_local_page().

With kmap_local_page(), the mappings are per thread, CPU local and not
globally visible. Furthermore, the mappings can be acquired from any
context (including interrupts).

Therefore, use kmap_local_page() in exec.c because these mappings are per
thread, CPU local, and not globally visible.

Tested with xfstests on a QEMU + KVM 32-bits VM booting a kernel with
HIGHMEM64GB enabled.

Suggested-by: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---
 fs/exec.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 0989fb8472a1..4a2129c0d422 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -583,11 +583,11 @@ static int copy_strings(int argc, struct user_arg_ptr argv,
 
 				if (kmapped_page) {
 					flush_dcache_page(kmapped_page);
-					kunmap(kmapped_page);
+					kunmap_local(kaddr);
 					put_arg_page(kmapped_page);
 				}
 				kmapped_page = page;
-				kaddr = kmap(kmapped_page);
+				kaddr = kmap_local_page(kmapped_page);
 				kpos = pos & PAGE_MASK;
 				flush_arg_page(bprm, kpos, kmapped_page);
 			}
@@ -601,7 +601,7 @@ static int copy_strings(int argc, struct user_arg_ptr argv,
 out:
 	if (kmapped_page) {
 		flush_dcache_page(kmapped_page);
-		kunmap(kmapped_page);
+		kunmap_local(kaddr);
 		put_arg_page(kmapped_page);
 	}
 	return ret;
@@ -883,11 +883,11 @@ int transfer_args_to_stack(struct linux_binprm *bprm,
 
 	for (index = MAX_ARG_PAGES - 1; index >= stop; index--) {
 		unsigned int offset = index == stop ? bprm->p & ~PAGE_MASK : 0;
-		char *src = kmap(bprm->page[index]) + offset;
+		char *src = kmap_local_page(bprm->page[index]) + offset;
 		sp -= PAGE_SIZE - offset;
 		if (copy_to_user((void *) sp, src, PAGE_SIZE - offset) != 0)
 			ret = -EFAULT;
-		kunmap(bprm->page[index]);
+		kunmap_local(src);
 		if (ret)
 			goto out;
 	}
@@ -1680,13 +1680,13 @@ int remove_arg_zero(struct linux_binprm *bprm)
 			ret = -EFAULT;
 			goto out;
 		}
-		kaddr = kmap_atomic(page);
+		kaddr = kmap_local_page(page);
 
 		for (; offset < PAGE_SIZE && kaddr[offset];
 				offset++, bprm->p++)
 			;
 
-		kunmap_atomic(kaddr);
+		kunmap_local(kaddr);
 		put_arg_page(page);
 	} while (offset == PAGE_SIZE);
 
-- 
2.36.1