[PATCH v3 0/3] Convert vmcore to use an iov_iter

[PATCH v3 0/3] Convert vmcore to use an iov_iter

[Matthew Wilcox (Oracle)]

For some reason several people have been sending bad patches to fix
compiler warnings in vmcore recently.  Here's how it should be done.
Compile-tested only on x86.  As noted in the first patch, s390 should
take this conversion a bit further, but I'm not inclined to do that
work myself.

v3:
 - Send the correct patches this time
v2:
 - Removed unnecessary kernel-doc
 - Included uio.h to fix compilation problems
 - Made read_from_oldmem_iter static to avoid compile warnings during the
   conversion
 - Use iov_iter_truncate() (Christoph)

Matthew Wilcox (Oracle) (3):
  vmcore: Convert copy_oldmem_page() to take an iov_iter
  vmcore: Convert __read_vmcore to use an iov_iter
  vmcore: Convert read_from_oldmem() to take an iov_iter

 arch/arm/kernel/crash_dump.c     |  27 +------
 arch/arm64/kernel/crash_dump.c   |  29 +------
 arch/ia64/kernel/crash_dump.c    |  32 +-------
 arch/mips/kernel/crash_dump.c    |  27 +------
 arch/powerpc/kernel/crash_dump.c |  35 ++-------
 arch/riscv/kernel/crash_dump.c   |  26 +------
 arch/s390/kernel/crash_dump.c    |  13 ++--
 arch/sh/kernel/crash_dump.c      |  29 ++-----
 arch/x86/kernel/crash_dump_32.c  |  29 +------
 arch/x86/kernel/crash_dump_64.c  |  48 ++++--------
 fs/proc/vmcore.c                 | 129 +++++++++++++------------------
 include/linux/crash_dump.h       |  19 ++---
 12 files changed, 122 insertions(+), 321 deletions(-)

-- 
2.33.0

[PATCH v3 1/3] vmcore: Convert copy_oldmem_page() to take an iov_iter

[Matthew Wilcox (Oracle)]

Instead of passing in a 'buf' and 'userbuf' argument, pass in an iov_iter.
s390 needs more work to pass the iov_iter down further, or refactor,
but I'd be more comfortable if someone who can test on s390 did that work.

It's more convenient to convert the whole of read_from_oldmem() to
take an iov_iter at the same time, so rename it to read_from_oldmem_iter()
and add a temporary read_from_oldmem() wrapper that creates an iov_iter.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 arch/arm/kernel/crash_dump.c     | 27 +++-------------
 arch/arm64/kernel/crash_dump.c   | 29 +++--------------
 arch/ia64/kernel/crash_dump.c    | 32 +++----------------
 arch/mips/kernel/crash_dump.c    | 27 +++-------------
 arch/powerpc/kernel/crash_dump.c | 35 +++------------------
 arch/riscv/kernel/crash_dump.c   | 26 +++------------
 arch/s390/kernel/crash_dump.c    | 13 +++++---
 arch/sh/kernel/crash_dump.c      | 29 +++--------------
 arch/x86/kernel/crash_dump_32.c  | 29 +++--------------
 arch/x86/kernel/crash_dump_64.c  | 41 +++++++-----------------
 fs/proc/vmcore.c                 | 54 ++++++++++++++++++++------------
 include/linux/crash_dump.h       |  9 +++---
 12 files changed, 91 insertions(+), 260 deletions(-)

diff --git a/arch/arm/kernel/crash_dump.c b/arch/arm/kernel/crash_dump.c
index 53cb92435392..938bd932df9a 100644
--- a/arch/arm/kernel/crash_dump.c
+++ b/arch/arm/kernel/crash_dump.c
@@ -14,22 +14,10 @@
 #include <linux/crash_dump.h>
 #include <linux/uaccess.h>
 #include <linux/io.h>
+#include <linux/uio.h>
 
-/**
- * copy_oldmem_page() - copy one page from old kernel memory
- * @pfn: page frame number to be copied
- * @buf: buffer where the copied page is placed
- * @csize: number of bytes to copy
- * @offset: offset in bytes into the page
- * @userbuf: if set, @buf is int he user address space
- *
- * This function copies one page from old kernel memory into buffer pointed by
- * @buf. If @buf is in userspace, set @userbuf to %1. Returns number of bytes
- * copied or negative error in case of failure.
- */
-ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
-			 size_t csize, unsigned long offset,
-			 int userbuf)
+ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
+			 size_t csize, unsigned long offset)
 {
 	void *vaddr;
 
@@ -40,14 +28,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 	if (!vaddr)
 		return -ENOMEM;
 
-	if (userbuf) {
-		if (copy_to_user(buf, vaddr + offset, csize)) {
-			iounmap(vaddr);
-			return -EFAULT;
-		}
-	} else {
-		memcpy(buf, vaddr + offset, csize);
-	}
+	csize = copy_to_iter(vaddr + offset, csize, iter);
 
 	iounmap(vaddr);
 	return csize;
diff --git a/arch/arm64/kernel/crash_dump.c b/arch/arm64/kernel/crash_dump.c
index 58303a9ec32c..670e4ce81822 100644
--- a/arch/arm64/kernel/crash_dump.c
+++ b/arch/arm64/kernel/crash_dump.c
@@ -9,25 +9,11 @@
 #include <linux/crash_dump.h>
 #include <linux/errno.h>
 #include <linux/io.h>
-#include <linux/memblock.h>
-#include <linux/uaccess.h>
+#include <linux/uio.h>
 #include <asm/memory.h>
 
-/**
- * copy_oldmem_page() - copy one page from old kernel memory
- * @pfn: page frame number to be copied
- * @buf: buffer where the copied page is placed
- * @csize: number of bytes to copy
- * @offset: offset in bytes into the page
- * @userbuf: if set, @buf is in a user address space
- *
- * This function copies one page from old kernel memory into buffer pointed by
- * @buf. If @buf is in userspace, set @userbuf to %1. Returns number of bytes
- * copied or negative error in case of failure.
- */
-ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
-			 size_t csize, unsigned long offset,
-			 int userbuf)
+ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
+			 size_t csize, unsigned long offset)
 {
 	void *vaddr;
 
@@ -38,14 +24,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 	if (!vaddr)
 		return -ENOMEM;
 
-	if (userbuf) {
-		if (copy_to_user((char __user *)buf, vaddr + offset, csize)) {
-			memunmap(vaddr);
-			return -EFAULT;
-		}
-	} else {
-		memcpy(buf, vaddr + offset, csize);
-	}
+	csize = copy_to_iter(vaddr + offset, csize, iter);
 
 	memunmap(vaddr);
 
diff --git a/arch/ia64/kernel/crash_dump.c b/arch/ia64/kernel/crash_dump.c
index 0ed3c3dee4cd..4ef68e2aa757 100644
--- a/arch/ia64/kernel/crash_dump.c
+++ b/arch/ia64/kernel/crash_dump.c
@@ -10,42 +10,18 @@
 #include <linux/errno.h>
 #include <linux/types.h>
 #include <linux/crash_dump.h>
-
+#include <linux/uio.h>
 #include <asm/page.h>
-#include <linux/uaccess.h>
 
-/**
- * copy_oldmem_page - copy one page from "oldmem"
- * @pfn: page frame number to be copied
- * @buf: target memory address for the copy; this can be in kernel address
- *	space or user address space (see @userbuf)
- * @csize: number of bytes to copy
- * @offset: offset in bytes into the page (based on pfn) to begin the copy
- * @userbuf: if set, @buf is in user address space, use copy_to_user(),
- *	otherwise @buf is in kernel address space, use memcpy().
- *
- * Copy a page from "oldmem". For this page, there is no pte mapped
- * in the current kernel. We stitch up a pte, similar to kmap_atomic.
- *
- * Calling copy_to_user() in atomic context is not desirable. Hence first
- * copying the data to a pre-allocated kernel page and then copying to user
- * space in non-atomic context.
- */
-ssize_t
-copy_oldmem_page(unsigned long pfn, char *buf,
-		size_t csize, unsigned long offset, int userbuf)
+ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
+		size_t csize, unsigned long offset)
 {
 	void  *vaddr;
 
 	if (!csize)
 		return 0;
 	vaddr = __va(pfn<<PAGE_SHIFT);
-	if (userbuf) {
-		if (copy_to_user(buf, (vaddr + offset), csize)) {
-			return -EFAULT;
-		}
-	} else
-		memcpy(buf, (vaddr + offset), csize);
+	csize = copy_to_iter(vaddr + offset, csize, iter);
 	return csize;
 }
 
diff --git a/arch/mips/kernel/crash_dump.c b/arch/mips/kernel/crash_dump.c
index 2e50f55185a6..6e50f4902409 100644
--- a/arch/mips/kernel/crash_dump.c
+++ b/arch/mips/kernel/crash_dump.c
@@ -1,22 +1,10 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/highmem.h>
 #include <linux/crash_dump.h>
+#include <linux/uio.h>
 
-/**
- * copy_oldmem_page - copy one page from "oldmem"
- * @pfn: page frame number to be copied
- * @buf: target memory address for the copy; this can be in kernel address
- *	space or user address space (see @userbuf)
- * @csize: number of bytes to copy
- * @offset: offset in bytes into the page (based on pfn) to begin the copy
- * @userbuf: if set, @buf is in user address space, use copy_to_user(),
- *	otherwise @buf is in kernel address space, use memcpy().
- *
- * Copy a page from "oldmem". For this page, there is no pte mapped
- * in the current kernel.
- */
-ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
-			 size_t csize, unsigned long offset, int userbuf)
+ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
+			 size_t csize, unsigned long offset)
 {
 	void  *vaddr;
 
@@ -24,14 +12,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 		return 0;
 
 	vaddr = kmap_local_pfn(pfn);
-
-	if (!userbuf) {
-		memcpy(buf, vaddr + offset, csize);
-	} else {
-		if (copy_to_user(buf, vaddr + offset, csize))
-			csize = -EFAULT;
-	}
-
+	csize = copy_to_iter(vaddr + offset, csize, iter);
 	kunmap_local(vaddr);
 
 	return csize;
diff --git a/arch/powerpc/kernel/crash_dump.c b/arch/powerpc/kernel/crash_dump.c
index 5693e1c67c2b..32b4a97f1b79 100644
--- a/arch/powerpc/kernel/crash_dump.c
+++ b/arch/powerpc/kernel/crash_dump.c
@@ -16,7 +16,7 @@
 #include <asm/kdump.h>
 #include <asm/prom.h>
 #include <asm/firmware.h>
-#include <linux/uaccess.h>
+#include <linux/uio.h>
 #include <asm/rtas.h>
 #include <asm/inst.h>
 
@@ -68,33 +68,8 @@ void __init setup_kdump_trampoline(void)
 }
 #endif /* CONFIG_NONSTATIC_KERNEL */
 
-static size_t copy_oldmem_vaddr(void *vaddr, char *buf, size_t csize,
-                               unsigned long offset, int userbuf)
-{
-	if (userbuf) {
-		if (copy_to_user((char __user *)buf, (vaddr + offset), csize))
-			return -EFAULT;
-	} else
-		memcpy(buf, (vaddr + offset), csize);
-
-	return csize;
-}
-
-/**
- * copy_oldmem_page - copy one page from "oldmem"
- * @pfn: page frame number to be copied
- * @buf: target memory address for the copy; this can be in kernel address
- *      space or user address space (see @userbuf)
- * @csize: number of bytes to copy
- * @offset: offset in bytes into the page (based on pfn) to begin the copy
- * @userbuf: if set, @buf is in user address space, use copy_to_user(),
- *      otherwise @buf is in kernel address space, use memcpy().
- *
- * Copy a page from "oldmem". For this page, there is no pte mapped
- * in the current kernel. We stitch up a pte, similar to kmap_atomic.
- */
-ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
-			size_t csize, unsigned long offset, int userbuf)
+ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
+			size_t csize, unsigned long offset)
 {
 	void  *vaddr;
 	phys_addr_t paddr;
@@ -107,10 +82,10 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 
 	if (memblock_is_region_memory(paddr, csize)) {
 		vaddr = __va(paddr);
-		csize = copy_oldmem_vaddr(vaddr, buf, csize, offset, userbuf);
+		csize = copy_to_iter(vaddr + offset, csize, iter);
 	} else {
 		vaddr = ioremap_cache(paddr, PAGE_SIZE);
-		csize = copy_oldmem_vaddr(vaddr, buf, csize, offset, userbuf);
+		csize = copy_to_iter(vaddr + offset, csize, iter);
 		iounmap(vaddr);
 	}
 
diff --git a/arch/riscv/kernel/crash_dump.c b/arch/riscv/kernel/crash_dump.c
index 86cc0ada5752..ea2158cee97b 100644
--- a/arch/riscv/kernel/crash_dump.c
+++ b/arch/riscv/kernel/crash_dump.c
@@ -7,22 +7,10 @@
 
 #include <linux/crash_dump.h>
 #include <linux/io.h>
+#include <linux/uio.h>
 
-/**
- * copy_oldmem_page() - copy one page from old kernel memory
- * @pfn: page frame number to be copied
- * @buf: buffer where the copied page is placed
- * @csize: number of bytes to copy
- * @offset: offset in bytes into the page
- * @userbuf: if set, @buf is in a user address space
- *
- * This function copies one page from old kernel memory into buffer pointed by
- * @buf. If @buf is in userspace, set @userbuf to %1. Returns number of bytes
- * copied or negative error in case of failure.
- */
-ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
-			 size_t csize, unsigned long offset,
-			 int userbuf)
+ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
+			 size_t csize, unsigned long offset)
 {
 	void *vaddr;
 
@@ -33,13 +21,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 	if (!vaddr)
 		return -ENOMEM;
 
-	if (userbuf) {
-		if (copy_to_user((char __user *)buf, vaddr + offset, csize)) {
-			memunmap(vaddr);
-			return -EFAULT;
-		}
-	} else
-		memcpy(buf, vaddr + offset, csize);
+	csize = copy_to_iter(vaddr + offset, csize, iter);
 
 	memunmap(vaddr);
 	return csize;
diff --git a/arch/s390/kernel/crash_dump.c b/arch/s390/kernel/crash_dump.c
index 785d54c9350c..9ada1dcde406 100644
--- a/arch/s390/kernel/crash_dump.c
+++ b/arch/s390/kernel/crash_dump.c
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/memblock.h>
 #include <linux/elf.h>
+#include <linux/uio.h>
 #include <asm/asm-offsets.h>
 #include <asm/os_info.h>
 #include <asm/elf.h>
@@ -214,8 +215,8 @@ static int copy_oldmem_user(void __user *dst, void *src, size_t count)
 /*
  * Copy one page from "oldmem"
  */
-ssize_t copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
-			 unsigned long offset, int userbuf)
+ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn, size_t csize,
+			 unsigned long offset)
 {
 	void *src;
 	int rc;
@@ -223,10 +224,12 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
 	if (!csize)
 		return 0;
 	src = (void *) (pfn << PAGE_SHIFT) + offset;
-	if (userbuf)
-		rc = copy_oldmem_user((void __force __user *) buf, src, csize);
+
+	/* XXX: pass the iov_iter down to a common function */
+	if (iter_is_iovec(iter))
+		rc = copy_oldmem_user(iter->iov->iov_base, src, csize);
 	else
-		rc = copy_oldmem_kernel((void *) buf, src, csize);
+		rc = copy_oldmem_kernel(iter->kvec->iov_base, src, csize);
 	return rc;
 }
 
diff --git a/arch/sh/kernel/crash_dump.c b/arch/sh/kernel/crash_dump.c
index 5b41b59698c1..277f44d8a298 100644
--- a/arch/sh/kernel/crash_dump.c
+++ b/arch/sh/kernel/crash_dump.c
@@ -8,23 +8,11 @@
 #include <linux/errno.h>
 #include <linux/crash_dump.h>
 #include <linux/io.h>
+#include <linux/uio.h>
 #include <linux/uaccess.h>
 
-/**
- * copy_oldmem_page - copy one page from "oldmem"
- * @pfn: page frame number to be copied
- * @buf: target memory address for the copy; this can be in kernel address
- *	space or user address space (see @userbuf)
- * @csize: number of bytes to copy
- * @offset: offset in bytes into the page (based on pfn) to begin the copy
- * @userbuf: if set, @buf is in user address space, use copy_to_user(),
- *	otherwise @buf is in kernel address space, use memcpy().
- *
- * Copy a page from "oldmem". For this page, there is no pte mapped
- * in the current kernel. We stitch up a pte, similar to kmap_atomic.
- */
-ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
-                               size_t csize, unsigned long offset, int userbuf)
+ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
+                               size_t csize, unsigned long offset)
 {
 	void  __iomem *vaddr;
 
@@ -32,15 +20,8 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 		return 0;
 
 	vaddr = ioremap(pfn << PAGE_SHIFT, PAGE_SIZE);
-
-	if (userbuf) {
-		if (copy_to_user((void __user *)buf, (vaddr + offset), csize)) {
-			iounmap(vaddr);
-			return -EFAULT;
-		}
-	} else
-	memcpy(buf, (vaddr + offset), csize);
-
+	csize = copy_to_iter(vaddr + offset, csize, iter);
 	iounmap(vaddr);
+
 	return csize;
 }
diff --git a/arch/x86/kernel/crash_dump_32.c b/arch/x86/kernel/crash_dump_32.c
index 5fcac46aaf6b..5f4ae5476e19 100644
--- a/arch/x86/kernel/crash_dump_32.c
+++ b/arch/x86/kernel/crash_dump_32.c
@@ -10,8 +10,7 @@
 #include <linux/errno.h>
 #include <linux/highmem.h>
 #include <linux/crash_dump.h>
-
-#include <linux/uaccess.h>
+#include <linux/uio.h>
 
 static inline bool is_crashed_pfn_valid(unsigned long pfn)
 {
@@ -29,21 +28,8 @@ static inline bool is_crashed_pfn_valid(unsigned long pfn)
 #endif
 }
 
-/**
- * copy_oldmem_page - copy one page from "oldmem"
- * @pfn: page frame number to be copied
- * @buf: target memory address for the copy; this can be in kernel address
- *	space or user address space (see @userbuf)
- * @csize: number of bytes to copy
- * @offset: offset in bytes into the page (based on pfn) to begin the copy
- * @userbuf: if set, @buf is in user address space, use copy_to_user(),
- *	otherwise @buf is in kernel address space, use memcpy().
- *
- * Copy a page from "oldmem". For this page, there might be no pte mapped
- * in the current kernel.
- */
-ssize_t copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
-			 unsigned long offset, int userbuf)
+ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn, size_t csize,
+			 unsigned long offset)
 {
 	void  *vaddr;
 
@@ -54,14 +40,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
 		return -EFAULT;
 
 	vaddr = kmap_local_pfn(pfn);
-
-	if (!userbuf) {
-		memcpy(buf, vaddr + offset, csize);
-	} else {
-		if (copy_to_user(buf, vaddr + offset, csize))
-			csize = -EFAULT;
-	}
-
+	csize = copy_to_iter(vaddr + offset, csize, iter);
 	kunmap_local(vaddr);
 
 	return csize;
diff --git a/arch/x86/kernel/crash_dump_64.c b/arch/x86/kernel/crash_dump_64.c
index a7f617a3981d..f922d51c9d1f 100644
--- a/arch/x86/kernel/crash_dump_64.c
+++ b/arch/x86/kernel/crash_dump_64.c
@@ -8,12 +8,12 @@
 
 #include <linux/errno.h>
 #include <linux/crash_dump.h>
-#include <linux/uaccess.h>
+#include <linux/uio.h>
 #include <linux/io.h>
 #include <linux/cc_platform.h>
 
-static ssize_t __copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
-				  unsigned long offset, int userbuf,
+static ssize_t __copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
+				  size_t csize, unsigned long offset,
 				  bool encrypted)
 {
 	void  *vaddr;
@@ -29,47 +29,28 @@ static ssize_t __copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
 	if (!vaddr)
 		return -ENOMEM;
 
-	if (userbuf) {
-		if (copy_to_user((void __user *)buf, vaddr + offset, csize)) {
-			iounmap((void __iomem *)vaddr);
-			return -EFAULT;
-		}
-	} else
-		memcpy(buf, vaddr + offset, csize);
+	csize = copy_to_iter(vaddr + offset, csize, iter);
 
 	set_iounmap_nonlazy();
 	iounmap((void __iomem *)vaddr);
 	return csize;
 }
 
-/**
- * copy_oldmem_page - copy one page of memory
- * @pfn: page frame number to be copied
- * @buf: target memory address for the copy; this can be in kernel address
- *	space or user address space (see @userbuf)
- * @csize: number of bytes to copy
- * @offset: offset in bytes into the page (based on pfn) to begin the copy
- * @userbuf: if set, @buf is in user address space, use copy_to_user(),
- *	otherwise @buf is in kernel address space, use memcpy().
- *
- * Copy a page from the old kernel's memory. For this page, there is no pte
- * mapped in the current kernel. We stitch up a pte, similar to kmap_atomic.
- */
-ssize_t copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
-			 unsigned long offset, int userbuf)
+ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn, size_t csize,
+			 unsigned long offset)
 {
-	return __copy_oldmem_page(pfn, buf, csize, offset, userbuf, false);
+	return __copy_oldmem_page(iter, pfn, csize, offset, false);
 }
 
-/**
+/*
  * copy_oldmem_page_encrypted - same as copy_oldmem_page() above but ioremap the
  * memory with the encryption mask set to accommodate kdump on SME-enabled
  * machines.
  */
-ssize_t copy_oldmem_page_encrypted(unsigned long pfn, char *buf, size_t csize,
-				   unsigned long offset, int userbuf)
+ssize_t copy_oldmem_page_encrypted(struct iov_iter *iter, unsigned long pfn,
+				   size_t csize, unsigned long offset)
 {
-	return __copy_oldmem_page(pfn, buf, csize, offset, userbuf, true);
+	return __copy_oldmem_page(iter, pfn, csize, offset, true);
 }
 
 ssize_t elfcorehdr_read(char *buf, size_t count, u64 *ppos)
diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 509f85148fee..958cad6476e6 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -26,6 +26,7 @@
 #include <linux/vmalloc.h>
 #include <linux/pagemap.h>
 #include <linux/uaccess.h>
+#include <linux/uio.h>
 #include <linux/cc_platform.h>
 #include <asm/io.h>
 #include "internal.h"
@@ -132,9 +133,8 @@ static int open_vmcore(struct inode *inode, struct file *file)
 }
 
 /* Reads a page from the oldmem device from given offset. */
-ssize_t read_from_oldmem(char *buf, size_t count,
-			 u64 *ppos, int userbuf,
-			 bool encrypted)
+static ssize_t read_from_oldmem_iter(struct iov_iter *iter, size_t count,
+			 u64 *ppos, bool encrypted)
 {
 	unsigned long pfn, offset;
 	size_t nr_bytes;
@@ -155,29 +155,23 @@ ssize_t read_from_oldmem(char *buf, size_t count,
 
 		/* If pfn is not ram, return zeros for sparse dump files */
 		if (!pfn_is_ram(pfn)) {
-			tmp = 0;
-			if (!userbuf)
-				memset(buf, 0, nr_bytes);
-			else if (clear_user(buf, nr_bytes))
-				tmp = -EFAULT;
+			tmp = iov_iter_zero(nr_bytes, iter);
 		} else {
 			if (encrypted)
-				tmp = copy_oldmem_page_encrypted(pfn, buf,
+				tmp = copy_oldmem_page_encrypted(iter, pfn,
 								 nr_bytes,
-								 offset,
-								 userbuf);
+								 offset);
 			else
-				tmp = copy_oldmem_page(pfn, buf, nr_bytes,
-						       offset, userbuf);
+				tmp = copy_oldmem_page(iter, pfn, nr_bytes,
+						       offset);
 		}
-		if (tmp < 0) {
+		if (tmp < nr_bytes) {
 			up_read(&vmcore_cb_rwsem);
-			return tmp;
+			return -EFAULT;
 		}
 
 		*ppos += nr_bytes;
 		count -= nr_bytes;
-		buf += nr_bytes;
 		read += nr_bytes;
 		++pfn;
 		offset = 0;
@@ -187,6 +181,27 @@ ssize_t read_from_oldmem(char *buf, size_t count,
 	return read;
 }
 
+ssize_t read_from_oldmem(char *buf, size_t count,
+			 u64 *ppos, int userbuf,
+			 bool encrypted)
+{
+	struct iov_iter iter;
+	struct iovec iov;
+	struct kvec kvec;
+
+	if (userbuf) {
+		iov.iov_base = (__force void __user *)buf;
+		iov.iov_len = count;
+		iov_iter_init(&iter, READ, &iov, 1, count);
+	} else {
+		kvec.iov_base = buf;
+		kvec.iov_len = count;
+		iov_iter_kvec(&iter, READ, &kvec, 1, count);
+	}
+
+	return read_from_oldmem_iter(&iter, count, ppos, encrypted);
+}
+
 /*
  * Architectures may override this function to allocate ELF header in 2nd kernel
  */
@@ -231,11 +246,10 @@ int __weak remap_oldmem_pfn_range(struct vm_area_struct *vma,
 /*
  * Architectures which support memory encryption override this.
  */
-ssize_t __weak
-copy_oldmem_page_encrypted(unsigned long pfn, char *buf, size_t csize,
-			   unsigned long offset, int userbuf)
+ssize_t __weak copy_oldmem_page_encrypted(struct iov_iter *iter,
+		unsigned long pfn, size_t csize, unsigned long offset)
 {
-	return copy_oldmem_page(pfn, buf, csize, offset, userbuf);
+	return copy_oldmem_page(iter, pfn, csize, offset);
 }
 
 /*
diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
index 620821549b23..a1cf7d5c03c7 100644
--- a/include/linux/crash_dump.h
+++ b/include/linux/crash_dump.h
@@ -24,11 +24,10 @@ extern int remap_oldmem_pfn_range(struct vm_area_struct *vma,
 				  unsigned long from, unsigned long pfn,
 				  unsigned long size, pgprot_t prot);
 
-extern ssize_t copy_oldmem_page(unsigned long, char *, size_t,
-						unsigned long, int);
-extern ssize_t copy_oldmem_page_encrypted(unsigned long pfn, char *buf,
-					  size_t csize, unsigned long offset,
-					  int userbuf);
+ssize_t copy_oldmem_page(struct iov_iter *i, unsigned long pfn, size_t csize,
+		unsigned long offset);
+ssize_t copy_oldmem_page_encrypted(struct iov_iter *iter, unsigned long pfn,
+				   size_t csize, unsigned long offset);
 
 void vmcore_cleanup(void);
 
-- 
2.33.0

[PATCH v3 2/3] vmcore: Convert __read_vmcore to use an iov_iter

[Matthew Wilcox (Oracle)]

This gets rid of copy_to() and let us use proc_read_iter() instead
of proc_read().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/proc/vmcore.c | 81 +++++++++++++++++-------------------------------
 1 file changed, 29 insertions(+), 52 deletions(-)

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 958cad6476e6..7b25f568d20d 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -252,22 +252,8 @@ ssize_t __weak copy_oldmem_page_encrypted(struct iov_iter *iter,
 	return copy_oldmem_page(iter, pfn, csize, offset);
 }
 
-/*
- * Copy to either kernel or user space
- */
-static int copy_to(void *target, void *src, size_t size, int userbuf)
-{
-	if (userbuf) {
-		if (copy_to_user((char __user *) target, src, size))
-			return -EFAULT;
-	} else {
-		memcpy(target, src, size);
-	}
-	return 0;
-}
-
 #ifdef CONFIG_PROC_VMCORE_DEVICE_DUMP
-static int vmcoredd_copy_dumps(void *dst, u64 start, size_t size, int userbuf)
+static int vmcoredd_copy_dumps(struct iov_iter *iter, u64 start, size_t size)
 {
 	struct vmcoredd_node *dump;
 	u64 offset = 0;
@@ -280,14 +266,13 @@ static int vmcoredd_copy_dumps(void *dst, u64 start, size_t size, int userbuf)
 		if (start < offset + dump->size) {
 			tsz = min(offset + (u64)dump->size - start, (u64)size);
 			buf = dump->buf + start - offset;
-			if (copy_to(dst, buf, tsz, userbuf)) {
+			if (copy_to_iter(buf, tsz, iter) < tsz) {
 				ret = -EFAULT;
 				goto out_unlock;
 			}
 
 			size -= tsz;
 			start += tsz;
-			dst += tsz;
 
 			/* Leave now if buffer filled already */
 			if (!size)
@@ -343,33 +328,28 @@ static int vmcoredd_mmap_dumps(struct vm_area_struct *vma, unsigned long dst,
 /* Read from the ELF header and then the crash dump. On error, negative value is
  * returned otherwise number of bytes read are returned.
  */
-static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
-			     int userbuf)
+static ssize_t __read_vmcore(struct iov_iter *iter, loff_t *fpos)
 {
 	ssize_t acc = 0, tmp;
 	size_t tsz;
 	u64 start;
 	struct vmcore *m = NULL;
 
-	if (buflen == 0 || *fpos >= vmcore_size)
+	if (iter->count == 0 || *fpos >= vmcore_size)
 		return 0;
 
-	/* trim buflen to not go beyond EOF */
-	if (buflen > vmcore_size - *fpos)
-		buflen = vmcore_size - *fpos;
+	iov_iter_truncate(iter, vmcore_size - *fpos);
 
 	/* Read ELF core header */
 	if (*fpos < elfcorebuf_sz) {
-		tsz = min(elfcorebuf_sz - (size_t)*fpos, buflen);
-		if (copy_to(buffer, elfcorebuf + *fpos, tsz, userbuf))
+		tsz = min(elfcorebuf_sz - (size_t)*fpos, iter->count);
+		if (copy_to_iter(elfcorebuf + *fpos, tsz, iter) < tsz)
 			return -EFAULT;
-		buflen -= tsz;
 		*fpos += tsz;
-		buffer += tsz;
 		acc += tsz;
 
 		/* leave now if filled buffer already */
-		if (buflen == 0)
+		if (iter->count == 0)
 			return acc;
 	}
 
@@ -390,35 +370,31 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
 		/* Read device dumps */
 		if (*fpos < elfcorebuf_sz + vmcoredd_orig_sz) {
 			tsz = min(elfcorebuf_sz + vmcoredd_orig_sz -
-				  (size_t)*fpos, buflen);
+				  (size_t)*fpos, iter->count);
 			start = *fpos - elfcorebuf_sz;
-			if (vmcoredd_copy_dumps(buffer, start, tsz, userbuf))
+			if (vmcoredd_copy_dumps(iter, start, tsz))
 				return -EFAULT;
 
-			buflen -= tsz;
 			*fpos += tsz;
-			buffer += tsz;
 			acc += tsz;
 
 			/* leave now if filled buffer already */
-			if (!buflen)
+			if (!iter->count)
 				return acc;
 		}
 #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
 
 		/* Read remaining elf notes */
-		tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)*fpos, buflen);
+		tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)*fpos, iter->count);
 		kaddr = elfnotes_buf + *fpos - elfcorebuf_sz - vmcoredd_orig_sz;
-		if (copy_to(buffer, kaddr, tsz, userbuf))
+		if (copy_to_iter(kaddr, tsz, iter) < tsz)
 			return -EFAULT;
 
-		buflen -= tsz;
 		*fpos += tsz;
-		buffer += tsz;
 		acc += tsz;
 
 		/* leave now if filled buffer already */
-		if (buflen == 0)
+		if (iter->count == 0)
 			return acc;
 	}
 
@@ -426,19 +402,17 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
 		if (*fpos < m->offset + m->size) {
 			tsz = (size_t)min_t(unsigned long long,
 					    m->offset + m->size - *fpos,
-					    buflen);
+					    iter->count);
 			start = m->paddr + *fpos - m->offset;
-			tmp = read_from_oldmem(buffer, tsz, &start,
-					       userbuf, cc_platform_has(CC_ATTR_MEM_ENCRYPT));
+			tmp = read_from_oldmem_iter(iter, tsz, &start,
+					cc_platform_has(CC_ATTR_MEM_ENCRYPT));
 			if (tmp < 0)
 				return tmp;
-			buflen -= tsz;
 			*fpos += tsz;
-			buffer += tsz;
 			acc += tsz;
 
 			/* leave now if filled buffer already */
-			if (buflen == 0)
+			if (iter->count == 0)
 				return acc;
 		}
 	}
@@ -446,15 +420,14 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
 	return acc;
 }
 
-static ssize_t read_vmcore(struct file *file, char __user *buffer,
-			   size_t buflen, loff_t *fpos)
+static ssize_t read_vmcore(struct kiocb *iocb, struct iov_iter *iter)
 {
-	return __read_vmcore((__force char *) buffer, buflen, fpos, 1);
+	return __read_vmcore(iter, &iocb->ki_pos);
 }
 
 /*
  * The vmcore fault handler uses the page cache and fills data using the
- * standard __vmcore_read() function.
+ * standard __read_vmcore() function.
  *
  * On s390 the fault handler is used for memory regions that can't be mapped
  * directly with remap_pfn_range().
@@ -464,9 +437,10 @@ static vm_fault_t mmap_vmcore_fault(struct vm_fault *vmf)
 #ifdef CONFIG_S390
 	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
 	pgoff_t index = vmf->pgoff;
+	struct iov_iter iter;
+	struct kvec kvec;
 	struct page *page;
 	loff_t offset;
-	char *buf;
 	int rc;
 
 	page = find_or_create_page(mapping, index, GFP_KERNEL);
@@ -474,8 +448,11 @@ static vm_fault_t mmap_vmcore_fault(struct vm_fault *vmf)
 		return VM_FAULT_OOM;
 	if (!PageUptodate(page)) {
 		offset = (loff_t) index << PAGE_SHIFT;
-		buf = __va((page_to_pfn(page) << PAGE_SHIFT));
-		rc = __read_vmcore(buf, PAGE_SIZE, &offset, 0);
+		kvec.iov_base = page_address(page);
+		kvec.iov_len = PAGE_SIZE;
+		iov_iter_kvec(&iter, READ, &kvec, 1, PAGE_SIZE);
+
+		rc = __read_vmcore(&iter, &offset);
 		if (rc < 0) {
 			unlock_page(page);
 			put_page(page);
@@ -725,7 +702,7 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)
 
 static const struct proc_ops vmcore_proc_ops = {
 	.proc_open	= open_vmcore,
-	.proc_read	= read_vmcore,
+	.proc_read_iter	= read_vmcore,
 	.proc_lseek	= default_llseek,
 	.proc_mmap	= mmap_vmcore,
 };
-- 
2.33.0

[PATCH v3 3/3] vmcore: Convert read_from_oldmem() to take an iov_iter

[Matthew Wilcox (Oracle)]

Remove the read_from_oldmem() wrapper introduced earlier and convert
all the remaining callers to pass an iov_iter.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 arch/x86/kernel/crash_dump_64.c |  7 +++++-
 fs/proc/vmcore.c                | 40 +++++++++++++--------------------
 include/linux/crash_dump.h      | 10 ++++-----
 3 files changed, 25 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kernel/crash_dump_64.c b/arch/x86/kernel/crash_dump_64.c
index f922d51c9d1f..0fa87648e55c 100644
--- a/arch/x86/kernel/crash_dump_64.c
+++ b/arch/x86/kernel/crash_dump_64.c
@@ -55,6 +55,11 @@ ssize_t copy_oldmem_page_encrypted(struct iov_iter *iter, unsigned long pfn,
 
 ssize_t elfcorehdr_read(char *buf, size_t count, u64 *ppos)
 {
-	return read_from_oldmem(buf, count, ppos, 0,
+	struct kvec kvec = { .iov_base = buf, .iov_len = count };
+	struct iov_iter iter;
+
+	iov_iter_kvec(&iter, READ, &kvec, 1, count);
+
+	return read_from_oldmem(&iter, count, ppos,
 				cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT));
 }
diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 7b25f568d20d..bee05b40196b 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -133,7 +133,7 @@ static int open_vmcore(struct inode *inode, struct file *file)
 }
 
 /* Reads a page from the oldmem device from given offset. */
-static ssize_t read_from_oldmem_iter(struct iov_iter *iter, size_t count,
+ssize_t read_from_oldmem(struct iov_iter *iter, size_t count,
 			 u64 *ppos, bool encrypted)
 {
 	unsigned long pfn, offset;
@@ -181,27 +181,6 @@ static ssize_t read_from_oldmem_iter(struct iov_iter *iter, size_t count,
 	return read;
 }
 
-ssize_t read_from_oldmem(char *buf, size_t count,
-			 u64 *ppos, int userbuf,
-			 bool encrypted)
-{
-	struct iov_iter iter;
-	struct iovec iov;
-	struct kvec kvec;
-
-	if (userbuf) {
-		iov.iov_base = (__force void __user *)buf;
-		iov.iov_len = count;
-		iov_iter_init(&iter, READ, &iov, 1, count);
-	} else {
-		kvec.iov_base = buf;
-		kvec.iov_len = count;
-		iov_iter_kvec(&iter, READ, &kvec, 1, count);
-	}
-
-	return read_from_oldmem_iter(&iter, count, ppos, encrypted);
-}
-
 /*
  * Architectures may override this function to allocate ELF header in 2nd kernel
  */
@@ -221,7 +200,12 @@ void __weak elfcorehdr_free(unsigned long long addr)
  */
 ssize_t __weak elfcorehdr_read(char *buf, size_t count, u64 *ppos)
 {
-	return read_from_oldmem(buf, count, ppos, 0, false);
+	struct kvec kvec = { .iov_base = buf, .iov_len = count };
+	struct iov_iter iter;
+
+	iov_iter_kvec(&iter, READ, &kvec, 1, count);
+
+	return read_from_oldmem(&iter, count, ppos, false);
 }
 
 /*
@@ -229,7 +213,13 @@ ssize_t __weak elfcorehdr_read(char *buf, size_t count, u64 *ppos)
  */
 ssize_t __weak elfcorehdr_read_notes(char *buf, size_t count, u64 *ppos)
 {
-	return read_from_oldmem(buf, count, ppos, 0, cc_platform_has(CC_ATTR_MEM_ENCRYPT));
+	struct kvec kvec = { .iov_base = buf, .iov_len = count };
+	struct iov_iter iter;
+
+	iov_iter_kvec(&iter, READ, &kvec, 1, count);
+
+	return read_from_oldmem(&iter, count, ppos,
+			cc_platform_has(CC_ATTR_MEM_ENCRYPT));
 }
 
 /*
@@ -404,7 +394,7 @@ static ssize_t __read_vmcore(struct iov_iter *iter, loff_t *fpos)
 					    m->offset + m->size - *fpos,
 					    iter->count);
 			start = m->paddr + *fpos - m->offset;
-			tmp = read_from_oldmem_iter(iter, tsz, &start,
+			tmp = read_from_oldmem(iter, tsz, &start,
 					cc_platform_has(CC_ATTR_MEM_ENCRYPT));
 			if (tmp < 0)
 				return tmp;
diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
index a1cf7d5c03c7..0f3a656293b0 100644
--- a/include/linux/crash_dump.h
+++ b/include/linux/crash_dump.h
@@ -134,13 +134,11 @@ static inline int vmcore_add_device_dump(struct vmcoredd_data *data)
 #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
 
 #ifdef CONFIG_PROC_VMCORE
-ssize_t read_from_oldmem(char *buf, size_t count,
-			 u64 *ppos, int userbuf,
-			 bool encrypted);
+ssize_t read_from_oldmem(struct iov_iter *iter, size_t count,
+			 u64 *ppos, bool encrypted);
 #else
-static inline ssize_t read_from_oldmem(char *buf, size_t count,
-				       u64 *ppos, int userbuf,
-				       bool encrypted)
+static inline ssize_t read_from_oldmem(struct iov_iter *iter, size_t count,
+				       u64 *ppos, bool encrypted)
 {
 	return -EOPNOTSUPP;
 }
-- 
2.33.0

Re: [PATCH v3 0/3] Convert vmcore to use an iov_iter

[Baoquan He]

On 12/13/21 at 02:39pm, Matthew Wilcox (Oracle) wrote:
> For some reason several people have been sending bad patches to fix
> compiler warnings in vmcore recently.  Here's how it should be done.
> Compile-tested only on x86.  As noted in the first patch, s390 should
> take this conversion a bit further, but I'm not inclined to do that
> work myself.

Add Philipp to the CC.

He used to work on s390 arch. Now he joins Redhat and will focus
on kexec/kdump. See if he has any thoughts on the s390 part of work, or
may reach out to s390 developer.

> 
> v3:
>  - Send the correct patches this time
> v2:
>  - Removed unnecessary kernel-doc
>  - Included uio.h to fix compilation problems
>  - Made read_from_oldmem_iter static to avoid compile warnings during the
>    conversion
>  - Use iov_iter_truncate() (Christoph)
> 
> Matthew Wilcox (Oracle) (3):
>   vmcore: Convert copy_oldmem_page() to take an iov_iter
>   vmcore: Convert __read_vmcore to use an iov_iter
>   vmcore: Convert read_from_oldmem() to take an iov_iter
> 
>  arch/arm/kernel/crash_dump.c     |  27 +------
>  arch/arm64/kernel/crash_dump.c   |  29 +------
>  arch/ia64/kernel/crash_dump.c    |  32 +-------
>  arch/mips/kernel/crash_dump.c    |  27 +------
>  arch/powerpc/kernel/crash_dump.c |  35 ++-------
>  arch/riscv/kernel/crash_dump.c   |  26 +------
>  arch/s390/kernel/crash_dump.c    |  13 ++--
>  arch/sh/kernel/crash_dump.c      |  29 ++-----
>  arch/x86/kernel/crash_dump_32.c  |  29 +------
>  arch/x86/kernel/crash_dump_64.c  |  48 ++++--------
>  fs/proc/vmcore.c                 | 129 +++++++++++++------------------
>  include/linux/crash_dump.h       |  19 ++---
>  12 files changed, 122 insertions(+), 321 deletions(-)
> 
> -- 
> 2.33.0
> 

Re: [PATCH v3 1/3] vmcore: Convert copy_oldmem_page() to take an iov_iter

[Baoquan He]

On 12/13/21 at 02:39pm, Matthew Wilcox (Oracle) wrote:
> Instead of passing in a 'buf' and 'userbuf' argument, pass in an iov_iter.
> s390 needs more work to pass the iov_iter down further, or refactor,
> but I'd be more comfortable if someone who can test on s390 did that work.
> 
> It's more convenient to convert the whole of read_from_oldmem() to
> take an iov_iter at the same time, so rename it to read_from_oldmem_iter()
> and add a temporary read_from_oldmem() wrapper that creates an iov_iter.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>


Thanks for making this to do an awesome clean up. This one looks good to
me.

Acked-by: Baoquan He <bhe@redhat.com>

...... 
> -/**
> - * copy_oldmem_page() - copy one page from old kernel memory
> - * @pfn: page frame number to be copied
> - * @buf: buffer where the copied page is placed
> - * @csize: number of bytes to copy
> - * @offset: offset in bytes into the page
> - * @userbuf: if set, @buf is int he user address space
> - *
> - * This function copies one page from old kernel memory into buffer pointed by
> - * @buf. If @buf is in userspace, set @userbuf to %1. Returns number of bytes
> - * copied or negative error in case of failure.
> - */
> -ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
> -			 size_t csize, unsigned long offset,
> -			 int userbuf)
> +ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
> +			 size_t csize, unsigned long offset)
                                ^^^^^^
I am curious why this parameter is called 'csize', but not 'size' directly.
This is not related to this patch, it's an old naming.

>  {
>  	void *vaddr;
>  
> @@ -40,14 +28,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
>  	if (!vaddr)
>  		return -ENOMEM;
>  
> -	if (userbuf) {
> -		if (copy_to_user(buf, vaddr + offset, csize)) {
> -			iounmap(vaddr);
> -			return -EFAULT;
> -		}
> -	} else {
> -		memcpy(buf, vaddr + offset, csize);
> -	}
> +	csize = copy_to_iter(vaddr + offset, csize, iter);
>  
>  	iounmap(vaddr);
>  	return csize;

Re: [PATCH v3 2/3] vmcore: Convert __read_vmcore to use an iov_iter

[Baoquan He]

On 12/13/21 at 02:39pm, Matthew Wilcox (Oracle) wrote:
> This gets rid of copy_to() and let us use proc_read_iter() instead
> of proc_read().
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Acked-by: Baoquan He <bhe@redhat.com>

> ---
>  fs/proc/vmcore.c | 81 +++++++++++++++++-------------------------------
>  1 file changed, 29 insertions(+), 52 deletions(-)
> 
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index 958cad6476e6..7b25f568d20d 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -252,22 +252,8 @@ ssize_t __weak copy_oldmem_page_encrypted(struct iov_iter *iter,
>  	return copy_oldmem_page(iter, pfn, csize, offset);
>  }
>  
> -/*
> - * Copy to either kernel or user space
> - */
> -static int copy_to(void *target, void *src, size_t size, int userbuf)
> -{
> -	if (userbuf) {
> -		if (copy_to_user((char __user *) target, src, size))
> -			return -EFAULT;
> -	} else {
> -		memcpy(target, src, size);
> -	}
> -	return 0;
> -}
> -
>  #ifdef CONFIG_PROC_VMCORE_DEVICE_DUMP
> -static int vmcoredd_copy_dumps(void *dst, u64 start, size_t size, int userbuf)
> +static int vmcoredd_copy_dumps(struct iov_iter *iter, u64 start, size_t size)
>  {
>  	struct vmcoredd_node *dump;
>  	u64 offset = 0;
> @@ -280,14 +266,13 @@ static int vmcoredd_copy_dumps(void *dst, u64 start, size_t size, int userbuf)
>  		if (start < offset + dump->size) {
>  			tsz = min(offset + (u64)dump->size - start, (u64)size);
>  			buf = dump->buf + start - offset;
> -			if (copy_to(dst, buf, tsz, userbuf)) {
> +			if (copy_to_iter(buf, tsz, iter) < tsz) {
>  				ret = -EFAULT;
>  				goto out_unlock;
>  			}
>  
>  			size -= tsz;
>  			start += tsz;
> -			dst += tsz;
>  
>  			/* Leave now if buffer filled already */
>  			if (!size)
> @@ -343,33 +328,28 @@ static int vmcoredd_mmap_dumps(struct vm_area_struct *vma, unsigned long dst,
>  /* Read from the ELF header and then the crash dump. On error, negative value is
>   * returned otherwise number of bytes read are returned.
>   */
> -static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
> -			     int userbuf)
> +static ssize_t __read_vmcore(struct iov_iter *iter, loff_t *fpos)
>  {
>  	ssize_t acc = 0, tmp;
>  	size_t tsz;
>  	u64 start;
>  	struct vmcore *m = NULL;
>  
> -	if (buflen == 0 || *fpos >= vmcore_size)
> +	if (iter->count == 0 || *fpos >= vmcore_size)
>  		return 0;
>  
> -	/* trim buflen to not go beyond EOF */
> -	if (buflen > vmcore_size - *fpos)
> -		buflen = vmcore_size - *fpos;
> +	iov_iter_truncate(iter, vmcore_size - *fpos);
>  
>  	/* Read ELF core header */
>  	if (*fpos < elfcorebuf_sz) {
> -		tsz = min(elfcorebuf_sz - (size_t)*fpos, buflen);
> -		if (copy_to(buffer, elfcorebuf + *fpos, tsz, userbuf))
> +		tsz = min(elfcorebuf_sz - (size_t)*fpos, iter->count);
> +		if (copy_to_iter(elfcorebuf + *fpos, tsz, iter) < tsz)
>  			return -EFAULT;
> -		buflen -= tsz;
>  		*fpos += tsz;
> -		buffer += tsz;
>  		acc += tsz;
>  
>  		/* leave now if filled buffer already */
> -		if (buflen == 0)
> +		if (iter->count == 0)
>  			return acc;
>  	}
>  
> @@ -390,35 +370,31 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
>  		/* Read device dumps */
>  		if (*fpos < elfcorebuf_sz + vmcoredd_orig_sz) {
>  			tsz = min(elfcorebuf_sz + vmcoredd_orig_sz -
> -				  (size_t)*fpos, buflen);
> +				  (size_t)*fpos, iter->count);
>  			start = *fpos - elfcorebuf_sz;
> -			if (vmcoredd_copy_dumps(buffer, start, tsz, userbuf))
> +			if (vmcoredd_copy_dumps(iter, start, tsz))
>  				return -EFAULT;
>  
> -			buflen -= tsz;
>  			*fpos += tsz;
> -			buffer += tsz;
>  			acc += tsz;
>  
>  			/* leave now if filled buffer already */
> -			if (!buflen)
> +			if (!iter->count)
>  				return acc;
>  		}
>  #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
>  
>  		/* Read remaining elf notes */
> -		tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)*fpos, buflen);
> +		tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)*fpos, iter->count);
>  		kaddr = elfnotes_buf + *fpos - elfcorebuf_sz - vmcoredd_orig_sz;
> -		if (copy_to(buffer, kaddr, tsz, userbuf))
> +		if (copy_to_iter(kaddr, tsz, iter) < tsz)
>  			return -EFAULT;
>  
> -		buflen -= tsz;
>  		*fpos += tsz;
> -		buffer += tsz;
>  		acc += tsz;
>  
>  		/* leave now if filled buffer already */
> -		if (buflen == 0)
> +		if (iter->count == 0)
>  			return acc;
>  	}
>  
> @@ -426,19 +402,17 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
>  		if (*fpos < m->offset + m->size) {
>  			tsz = (size_t)min_t(unsigned long long,
>  					    m->offset + m->size - *fpos,
> -					    buflen);
> +					    iter->count);
>  			start = m->paddr + *fpos - m->offset;
> -			tmp = read_from_oldmem(buffer, tsz, &start,
> -					       userbuf, cc_platform_has(CC_ATTR_MEM_ENCRYPT));
> +			tmp = read_from_oldmem_iter(iter, tsz, &start,
> +					cc_platform_has(CC_ATTR_MEM_ENCRYPT));
>  			if (tmp < 0)
>  				return tmp;
> -			buflen -= tsz;
>  			*fpos += tsz;
> -			buffer += tsz;
>  			acc += tsz;
>  
>  			/* leave now if filled buffer already */
> -			if (buflen == 0)
> +			if (iter->count == 0)
>  				return acc;
>  		}
>  	}
> @@ -446,15 +420,14 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
>  	return acc;
>  }
>  
> -static ssize_t read_vmcore(struct file *file, char __user *buffer,
> -			   size_t buflen, loff_t *fpos)
> +static ssize_t read_vmcore(struct kiocb *iocb, struct iov_iter *iter)
>  {
> -	return __read_vmcore((__force char *) buffer, buflen, fpos, 1);
> +	return __read_vmcore(iter, &iocb->ki_pos);
>  }
>  
>  /*
>   * The vmcore fault handler uses the page cache and fills data using the
> - * standard __vmcore_read() function.
> + * standard __read_vmcore() function.
>   *
>   * On s390 the fault handler is used for memory regions that can't be mapped
>   * directly with remap_pfn_range().
> @@ -464,9 +437,10 @@ static vm_fault_t mmap_vmcore_fault(struct vm_fault *vmf)
>  #ifdef CONFIG_S390
>  	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
>  	pgoff_t index = vmf->pgoff;
> +	struct iov_iter iter;
> +	struct kvec kvec;
>  	struct page *page;
>  	loff_t offset;
> -	char *buf;
>  	int rc;
>  
>  	page = find_or_create_page(mapping, index, GFP_KERNEL);
> @@ -474,8 +448,11 @@ static vm_fault_t mmap_vmcore_fault(struct vm_fault *vmf)
>  		return VM_FAULT_OOM;
>  	if (!PageUptodate(page)) {
>  		offset = (loff_t) index << PAGE_SHIFT;
> -		buf = __va((page_to_pfn(page) << PAGE_SHIFT));
> -		rc = __read_vmcore(buf, PAGE_SIZE, &offset, 0);
> +		kvec.iov_base = page_address(page);
> +		kvec.iov_len = PAGE_SIZE;
> +		iov_iter_kvec(&iter, READ, &kvec, 1, PAGE_SIZE);
> +
> +		rc = __read_vmcore(&iter, &offset);
>  		if (rc < 0) {
>  			unlock_page(page);
>  			put_page(page);
> @@ -725,7 +702,7 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)
>  
>  static const struct proc_ops vmcore_proc_ops = {
>  	.proc_open	= open_vmcore,
> -	.proc_read	= read_vmcore,
> +	.proc_read_iter	= read_vmcore,
>  	.proc_lseek	= default_llseek,
>  	.proc_mmap	= mmap_vmcore,
>  };
> -- 
> 2.33.0
> 

Re: [PATCH v3 0/3] Convert vmcore to use an iov_iter

[Baoquan He]

On 12/13/21 at 02:39pm, Matthew Wilcox (Oracle) wrote:
> For some reason several people have been sending bad patches to fix
> compiler warnings in vmcore recently.  Here's how it should be done.
> Compile-tested only on x86.  As noted in the first patch, s390 should
> take this conversion a bit further, but I'm not inclined to do that
> work myself.

Ack this series of patches.

Acked-by: Baoquan He <bhe@redhat.com>

> 
> v3:
>  - Send the correct patches this time
> v2:
>  - Removed unnecessary kernel-doc
>  - Included uio.h to fix compilation problems
>  - Made read_from_oldmem_iter static to avoid compile warnings during the
>    conversion
>  - Use iov_iter_truncate() (Christoph)
> 
> Matthew Wilcox (Oracle) (3):
>   vmcore: Convert copy_oldmem_page() to take an iov_iter
>   vmcore: Convert __read_vmcore to use an iov_iter
>   vmcore: Convert read_from_oldmem() to take an iov_iter
> 
>  arch/arm/kernel/crash_dump.c     |  27 +------
>  arch/arm64/kernel/crash_dump.c   |  29 +------
>  arch/ia64/kernel/crash_dump.c    |  32 +-------
>  arch/mips/kernel/crash_dump.c    |  27 +------
>  arch/powerpc/kernel/crash_dump.c |  35 ++-------
>  arch/riscv/kernel/crash_dump.c   |  26 +------
>  arch/s390/kernel/crash_dump.c    |  13 ++--
>  arch/sh/kernel/crash_dump.c      |  29 ++-----
>  arch/x86/kernel/crash_dump_32.c  |  29 +------
>  arch/x86/kernel/crash_dump_64.c  |  48 ++++--------
>  fs/proc/vmcore.c                 | 129 +++++++++++++------------------
>  include/linux/crash_dump.h       |  19 ++---
>  12 files changed, 122 insertions(+), 321 deletions(-)
> 
> -- 
> 2.33.0
> 

Re: [PATCH v3 1/3] vmcore: Convert copy_oldmem_page() to take an iov_iter

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v3 2/3] vmcore: Convert __read_vmcore to use an iov_iter

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v3 3/3] vmcore: Convert read_from_oldmem() to take an iov_iter

[Christoph Hellwig]

On Mon, Dec 13, 2021 at 02:39:27PM +0000, Matthew Wilcox (Oracle) wrote:
> Remove the read_from_oldmem() wrapper introduced earlier and convert
> all the remaining callers to pass an iov_iter.

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v3 0/3] Convert vmcore to use an iov_iter

[Al Viro]

On Mon, Dec 13, 2021 at 02:39:24PM +0000, Matthew Wilcox (Oracle) wrote:
> For some reason several people have been sending bad patches to fix
> compiler warnings in vmcore recently.  Here's how it should be done.
> Compile-tested only on x86.  As noted in the first patch, s390 should
> take this conversion a bit further, but I'm not inclined to do that
> work myself.

A couple of notes: please, use iov_iter_count(i) instead of open-coding
i->count.  And there's a preexisting nastiness in read_vmcore() -
generally, a fault halfway through the read() is treated as a short read,
rather than -EFAULT...

Re: [PATCH v3 0/3] Convert vmcore to use an iov_iter

[Baoquan He]

Hi,

On 01/01/22 at 12:36am, Al Viro wrote:
> On Mon, Dec 13, 2021 at 02:39:24PM +0000, Matthew Wilcox (Oracle) wrote:
> > For some reason several people have been sending bad patches to fix
> > compiler warnings in vmcore recently.  Here's how it should be done.
> > Compile-tested only on x86.  As noted in the first patch, s390 should
> > take this conversion a bit further, but I'm not inclined to do that
> > work myself.
> 
> A couple of notes: please, use iov_iter_count(i) instead of open-coding
> i->count.  And there's a preexisting nastiness in read_vmcore() -
> generally, a fault halfway through the read() is treated as a short read,
> rather than -EFAULT...

Willy must be busy with those tons of folio patches, since I have acked
this patchset, I will update them as per your comment and repost them
with v4.

Thanks for checking.

Re: [PATCH v3 0/3] Convert vmcore to use an iov_iter

[Baoquan He]

On 01/01/22 at 12:36am, Al Viro wrote:
> On Mon, Dec 13, 2021 at 02:39:24PM +0000, Matthew Wilcox (Oracle) wrote:
> > For some reason several people have been sending bad patches to fix
> > compiler warnings in vmcore recently.  Here's how it should be done.
> > Compile-tested only on x86.  As noted in the first patch, s390 should
> > take this conversion a bit further, but I'm not inclined to do that
> > work myself.
> 
> A couple of notes: please, use iov_iter_count(i) instead of open-coding
> i->count.  And there's a preexisting nastiness in read_vmcore() -
> generally, a fault halfway through the read() is treated as a short read,
> rather than -EFAULT...

Sorry for being late to work on this.

While checking it, I noticed it's generic to return -EFAULT in kernel.
E.g in kernfs_file_read_iter(). Even though 'man 3 read' does give the
same words as you noted.

However, the manpage says the less then nbyte case happened just in case
the number of bytes left in the file is less than nbyte. The returning
-EFAULT in read_vmcore() seems to be a little different and not
satisfying the condition, because the left bytes should be greater than
the nbyte when reading out the elf note, or the middle of the vmcore. So
we should leave it as is?

Abstract from man page of read:
====
Upon successful completion, where nbyte is greater than 0, read() shall mark for update the last data access timestamp of the
file, and shall return the number of bytes read.  This number shall never be greater than nbyte.  The value returned  may  be
less  than  nbyte if the number of bytes left in the file is less than nbyte, if the read() request was interrupted by a sig‐
nal, or if the file is a pipe or FIFO or special file and has fewer than nbyte bytes immediately available for  reading.  For
example, a read() from a file associated with a terminal may return one typed line of data.
====