Re: [RFC PATCH -next V2 7/7] arm64: add pagecache reading to machine check safe
From: Tong Tiangen
Date: Thu Apr 07 2022 - 22:44:12 EST
在 2022/4/7 23:53, Robin Murphy 写道:
On 2022-04-07 15:56, Tong Tiangen wrote:
在 2022/4/6 19:27, Mark Rutland 写道:
On Wed, Apr 06, 2022 at 09:13:11AM +0000, Tong Tiangen wrote:
When user process reading file, the data is cached in pagecache and
the data belongs to the user process, When machine check error is
encountered during pagecache reading, killing the user process and
isolate the user page with hardware memory errors is a more reasonable
choice than kernel panic.
The __arch_copy_mc_to_user() in copy_to_user_mc.S is largely borrows
from __arch_copy_to_user() in copy_to_user.S and the main difference
is __arch_copy_mc_to_user() add the extable entry to support machine
check safe.
As with prior patches, *why* is the distinction necessary?
This patch adds a bunch of conditional logic, but *structurally* it
doesn't
alter the handling to be substantially different for the MC and
non-MC cases.
This seems like pointless duplication that just makes it harder to
maintain
this code.
Thanks,
Mark.
Agreed, The implementation here looks a little ugly and harder to
maintain.
The purpose of my doing this is not all copy_to_user can be recovered.
A memory error is consumed when reading pagecache using copy_to_user.
I think in this scenario, only the process is affected because it
can't read
pagecache data correctly. Just kill the process and don't need the whole
kernel panic.
So I need two different copy_to_user implementation, one is existing
__arch_copy_to_user,
this function will panic when consuming memory errors. The other one
is this new helper
__arch_copy_mc_to_user, this interface is used when reading pagecache.
It can recover from
consume memory error.
OK, but do we really need two almost-identical implementations of every
function where the only difference is how the exception table entries
are annotated? Could the exception handler itself just figure out who
owns the page where the fault occurred and decide what action to take as
appropriate?
Robin.
Thank you, Robin.
I added this call path in this patchset: do_sea() -> fixup_exception(),
the purpose is to provide a chance for sea fault to fixup (refer patch
3/7).
If fixup successful, panic can be avoided. Otherwise, panic can be
eliminated according to the original logic.
fixup_exception() will set regs->pc and jump to regs->pc when the
context recovery of an exception occurs.
If mc-safe-fixup added to __arch_copy_to_user(), in *non pagecache
reading* scenario encount memory error when call __arch_copy_to_user() ,
do_sea() -> fixup_exception() will not return fail and will miss the
panic logic in do_sea().
So I add new helper __arch_copy_mc_to_user() and add mc-safe-fixup to
this helper, which can be used in the required scenarios. At present,
there is only one pagecache reading scenario, other scenarios need to be
developed.
This is my current confusion. Of course, I will think about the solution
to solve the duplicate code problem.
Thanks,
Tong.
In future, if find a scenario use copy_to_user can also be recovered,
we can also use this mc
safe helper instead it.
Thanks,
Tong.
In _copy_page_to_iter(), machine check safe only considered ITER_IOVEC
which is used by pagecache reading.
Signed-off-by: Tong Tiangen <tongtiangen@xxxxxxxxxx>
---
arch/arm64/include/asm/uaccess.h | 15 ++++++
arch/arm64/lib/Makefile | 2 +-
arch/arm64/lib/copy_to_user_mc.S | 78 +++++++++++++++++++++++++++++
include/linux/uio.h | 9 +++-
lib/iov_iter.c | 85
+++++++++++++++++++++++++-------
5 files changed, 170 insertions(+), 19 deletions(-)
create mode 100644 arch/arm64/lib/copy_to_user_mc.S
diff --git a/arch/arm64/include/asm/uaccess.h
b/arch/arm64/include/asm/uaccess.h
index 24b662407fbd..f0d5e811165a 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -448,6 +448,21 @@ extern long strncpy_from_user(char *dest, const
char __user *src, long count);
extern __must_check long strnlen_user(const char __user *str, long
n);
+#ifdef CONFIG_ARCH_HAS_COPY_MC
+extern unsigned long __must_check __arch_copy_mc_to_user(void
__user *to,
+ const void *from, unsigned long n);
+static inline unsigned long __must_check
+copy_mc_to_user(void __user *to, const void *from, unsigned long n)
+{
+ uaccess_ttbr0_enable();
+ n = __arch_copy_mc_to_user(__uaccess_mask_ptr(to), from, n);
+ uaccess_ttbr0_disable();
+
+ return n;
+}
+#define copy_mc_to_user copy_mc_to_user
+#endif
+
#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
struct page;
void memcpy_page_flushcache(char *to, struct page *page, size_t
offset, size_t len);
diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index 29c578414b12..9b3571227fb4 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -23,4 +23,4 @@ obj-$(CONFIG_ARM64_MTE) += mte.o
obj-$(CONFIG_KASAN_SW_TAGS) += kasan_sw_tags.o
-obj-$(CONFIG_ARCH_HAS_CPY_MC) += copy_page_mc.o
+obj-$(CONFIG_ARCH_HAS_COPY_MC) += copy_page_mc.o copy_to_user_mc.o
diff --git a/arch/arm64/lib/copy_to_user_mc.S
b/arch/arm64/lib/copy_to_user_mc.S
new file mode 100644
index 000000000000..9d228ff15446
--- /dev/null
+++ b/arch/arm64/lib/copy_to_user_mc.S
@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2012 ARM Ltd.
+ */
+
+#include <linux/linkage.h>
+
+#include <asm/asm-uaccess.h>
+#include <asm/assembler.h>
+#include <asm/cache.h>
+
+/*
+ * Copy to user space from a kernel buffer (alignment handled by
the hardware)
+ *
+ * Parameters:
+ * x0 - to
+ * x1 - from
+ * x2 - n
+ * Returns:
+ * x0 - bytes not copied
+ */
+ .macro ldrb1 reg, ptr, val
+ 1000: ldrb \reg, [\ptr], \val;
+ _asm_extable_mc 1000b, 9998f;
+ .endm
+
+ .macro strb1 reg, ptr, val
+ user_ldst_mc 9998f, sttrb, \reg, \ptr, \val
+ .endm
+
+ .macro ldrh1 reg, ptr, val
+ 1001: ldrh \reg, [\ptr], \val;
+ _asm_extable_mc 1001b, 9998f;
+ .endm
+
+ .macro strh1 reg, ptr, val
+ user_ldst_mc 9997f, sttrh, \reg, \ptr, \val
+ .endm
+
+ .macro ldr1 reg, ptr, val
+ 1002: ldr \reg, [\ptr], \val;
+ _asm_extable_mc 1002b, 9998f;
+ .endm
+
+ .macro str1 reg, ptr, val
+ user_ldst_mc 9997f, sttr, \reg, \ptr, \val
+ .endm
+
+ .macro ldp1 reg1, reg2, ptr, val
+ 1003: ldp \reg1, \reg2, [\ptr], \val;
+ _asm_extable_mc 1003b, 9998f;
+ .endm
+
+ .macro stp1 reg1, reg2, ptr, val
+ user_stp 9997f, \reg1, \reg2, \ptr, \val
+ .endm
+
+end .req x5
+srcin .req x15
+SYM_FUNC_START(__arch_copy_mc_to_user)
+ add end, x0, x2
+ mov srcin, x1
+#include "copy_template.S"
+ mov x0, #0
+ ret
+
+ // Exception fixups
+9997: cbz x0, 9998f // Check machine check exception
+ cmp dst, dstin
+ b.ne 9998f
+ // Before being absolutely sure we couldn't copy anything, try
harder
+ ldrb tmp1w, [srcin]
+USER(9998f, sttrb tmp1w, [dst])
+ add dst, dst, #1
+9998: sub x0, end, dst // bytes not copied
+ ret
+SYM_FUNC_END(__arch_copy_mc_to_user)
+EXPORT_SYMBOL(__arch_copy_mc_to_user)
diff --git a/include/linux/uio.h b/include/linux/uio.h
index 739285fe5a2f..539d9ee9b032 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -147,10 +147,17 @@ size_t _copy_to_iter(const void *addr, size_t
bytes, struct iov_iter *i);
size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct
iov_iter *i);
+#ifdef CONFIG_ARCH_HAS_COPY_MC
+size_t copy_mc_page_to_iter(struct page *page, size_t offset,
size_t bytes,
+ struct iov_iter *i);
+#else
+#define copy_mc_page_to_iter copy_page_to_iter
+#endif
+
static inline size_t copy_folio_to_iter(struct folio *folio,
size_t offset,
size_t bytes, struct iov_iter *i)
{
- return copy_page_to_iter(&folio->page, offset, bytes, i);
+ return copy_mc_page_to_iter(&folio->page, offset, bytes, i);
}
static __always_inline __must_check
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 6dd5330f7a99..2c5f3bb6391d 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -157,6 +157,19 @@ static int copyout(void __user *to, const void
*from, size_t n)
return n;
}
+#ifdef CONFIG_ARCH_HAS_COPY_MC
+static int copyout_mc(void __user *to, const void *from, size_t n)
+{
+ if (access_ok(to, n)) {
+ instrument_copy_to_user(to, from, n);
+ n = copy_mc_to_user((__force void *) to, from, n);
+ }
+ return n;
+}
+#else
+#define copyout_mc copyout
+#endif
+
static int copyin(void *to, const void __user *from, size_t n)
{
if (should_fail_usercopy())
@@ -169,7 +182,7 @@ static int copyin(void *to, const void __user
*from, size_t n)
}
static size_t copy_page_to_iter_iovec(struct page *page, size_t
offset, size_t bytes,
- struct iov_iter *i)
+ struct iov_iter *i, bool mc_safe)
{
size_t skip, copy, left, wanted;
const struct iovec *iov;
@@ -194,7 +207,10 @@ static size_t copy_page_to_iter_iovec(struct
page *page, size_t offset, size_t b
from = kaddr + offset;
/* first chunk, usually the only one */
- left = copyout(buf, from, copy);
+ if (mc_safe)
+ left = copyout_mc(buf, from, copy);
+ else
+ left = copyout(buf, from, copy);
copy -= left;
skip += copy;
from += copy;
@@ -204,7 +220,10 @@ static size_t copy_page_to_iter_iovec(struct
page *page, size_t offset, size_t b
iov++;
buf = iov->iov_base;
copy = min(bytes, iov->iov_len);
- left = copyout(buf, from, copy);
+ if (mc_safe)
+ left = copyout_mc(buf, from, copy);
+ else
+ left = copyout(buf, from, copy);
copy -= left;
skip = copy;
from += copy;
@@ -223,7 +242,10 @@ static size_t copy_page_to_iter_iovec(struct
page *page, size_t offset, size_t b
kaddr = kmap(page);
from = kaddr + offset;
- left = copyout(buf, from, copy);
+ if (mc_safe)
+ left = copyout_mc(buf, from, copy);
+ else
+ left = copyout(buf, from, copy);
copy -= left;
skip += copy;
from += copy;
@@ -232,7 +254,10 @@ static size_t copy_page_to_iter_iovec(struct
page *page, size_t offset, size_t b
iov++;
buf = iov->iov_base;
copy = min(bytes, iov->iov_len);
- left = copyout(buf, from, copy);
+ if (mc_safe)
+ left = copyout_mc(buf, from, copy);
+ else
+ left = copyout(buf, from, copy);
copy -= left;
skip = copy;
from += copy;
@@ -674,15 +699,6 @@ size_t _copy_to_iter(const void *addr, size_t
bytes, struct iov_iter *i)
EXPORT_SYMBOL(_copy_to_iter);
#ifdef CONFIG_ARCH_HAS_COPY_MC
-static int copyout_mc(void __user *to, const void *from, size_t n)
-{
- if (access_ok(to, n)) {
- instrument_copy_to_user(to, from, n);
- n = copy_mc_to_user((__force void *) to, from, n);
- }
- return n;
-}
-
static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes,
struct iov_iter *i)
{
@@ -846,10 +862,10 @@ static inline bool page_copy_sane(struct page
*page, size_t offset, size_t n)
}
static size_t __copy_page_to_iter(struct page *page, size_t
offset, size_t bytes,
- struct iov_iter *i)
+ struct iov_iter *i, bool mc_safe)
{
if (likely(iter_is_iovec(i)))
- return copy_page_to_iter_iovec(page, offset, bytes, i);
+ return copy_page_to_iter_iovec(page, offset, bytes, i,
mc_safe);
if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) ||
iov_iter_is_xarray(i)) {
void *kaddr = kmap_local_page(page);
size_t wanted = _copy_to_iter(kaddr + offset, bytes, i);
@@ -878,7 +894,7 @@ size_t copy_page_to_iter(struct page *page,
size_t offset, size_t bytes,
offset %= PAGE_SIZE;
while (1) {
size_t n = __copy_page_to_iter(page, offset,
- min(bytes, (size_t)PAGE_SIZE - offset), i);
+ min(bytes, (size_t)PAGE_SIZE - offset), i, false);
res += n;
bytes -= n;
if (!bytes || !n)
@@ -893,6 +909,41 @@ size_t copy_page_to_iter(struct page *page,
size_t offset, size_t bytes,
}
EXPORT_SYMBOL(copy_page_to_iter);
+#ifdef CONFIG_ARCH_HAS_COPY_MC
+/**
+ * copy_mc_page_to_iter - copy page to iter with source memory
error exception handling.
+ *
+ * The filemap_read deploys this for pagecache reading and the main
differences between
+ * this and typical copy_page_to_iter() is call __copy_page_to_iter
with mc_safe true.
+ *
+ * Return: number of bytes copied (may be %0)
+ */
+size_t copy_mc_page_to_iter(struct page *page, size_t offset,
size_t bytes,
+ struct iov_iter *i)
+{
+ size_t res = 0;
+
+ if (unlikely(!page_copy_sane(page, offset, bytes)))
+ return 0;
+ page += offset / PAGE_SIZE; // first subpage
+ offset %= PAGE_SIZE;
+ while (1) {
+ size_t n = __copy_page_to_iter(page, offset,
+ min(bytes, (size_t)PAGE_SIZE - offset), i, true);
+ res += n;
+ bytes -= n;
+ if (!bytes || !n)
+ break;
+ offset += n;
+ if (offset == PAGE_SIZE) {
+ page++;
+ offset = 0;
+ }
+ }
+ return res;
+}
+#endif
+
size_t copy_page_from_iter(struct page *page, size_t offset,
size_t bytes,
struct iov_iter *i)
{
--
2.18.0.huawei.25
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