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Subject[PATCH v7 3/5] vmcore: Introduce remap_oldmem_pfn_range()
Date
For zfcpdump we can't map the HSA storage because it is only available
via a read interface. Therefore, for the new vmcore mmap feature we have
introduce a new mechanism to create mappings on demand.

This patch introduces a new architecture function remap_oldmem_pfn_range()
that should be used to create mappings with remap_pfn_range() for oldmem
areas that can be directly mapped. For zfcpdump this is everything besides
of the HSA memory. For the areas that are not mapped by remap_oldmem_pfn_range()
a generic vmcore a new generic vmcore fault handler mmap_vmcore_fault()
is called.

This handler works as follows:

* Get already available or new page from page cache (find_or_create_page)
* Check if /proc/vmcore page is filled with data (PageUptodate)
* If yes:
Return that page
* If no:
Fill page using __vmcore_read(), set PageUptodate, and return page

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
---
fs/proc/vmcore.c | 91 ++++++++++++++++++++++++++++++++++++++++++----
include/linux/crash_dump.h | 3 ++
2 files changed, 86 insertions(+), 8 deletions(-)

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index d2036df..532808e 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -21,6 +21,7 @@
#include <linux/crash_dump.h>
#include <linux/list.h>
#include <linux/vmalloc.h>
+#include <linux/pagemap.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include "internal.h"
@@ -153,11 +154,35 @@ ssize_t __weak elfcorehdr_read_notes(char *buf, size_t count, u64 *ppos)
return read_from_oldmem(buf, count, ppos, 0);
}

+/*
+ * Architectures may override this function to map oldmem
+ */
+int __weak remap_oldmem_pfn_range(struct vm_area_struct *vma,
+ unsigned long from, unsigned long pfn,
+ unsigned long size, pgprot_t prot)
+{
+ return remap_pfn_range(vma, from, pfn, size, prot);
+}
+
+/*
+ * 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(target, src, size))
+ return -EFAULT;
+ } else {
+ memcpy(target, src, size);
+ }
+ return 0;
+}
+
/* 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(struct file *file, char __user *buffer,
- size_t buflen, loff_t *fpos)
+static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
+ int userbuf)
{
ssize_t acc = 0, tmp;
size_t tsz;
@@ -174,7 +199,7 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
/* Read ELF core header */
if (*fpos < elfcorebuf_sz) {
tsz = min(elfcorebuf_sz - (size_t)*fpos, buflen);
- if (copy_to_user(buffer, elfcorebuf + *fpos, tsz))
+ if (copy_to(buffer, elfcorebuf + *fpos, tsz, userbuf))
return -EFAULT;
buflen -= tsz;
*fpos += tsz;
@@ -192,7 +217,7 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,

tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)*fpos, buflen);
kaddr = elfnotes_buf + *fpos - elfcorebuf_sz;
- if (copy_to_user(buffer, kaddr, tsz))
+ if (copy_to(buffer, kaddr, tsz, userbuf))
return -EFAULT;
buflen -= tsz;
*fpos += tsz;
@@ -208,7 +233,7 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
if (*fpos < m->offset + m->size) {
tsz = min_t(size_t, m->offset + m->size - *fpos, buflen);
start = m->paddr + *fpos - m->offset;
- tmp = read_from_oldmem(buffer, tsz, &start, 1);
+ tmp = read_from_oldmem(buffer, tsz, &start, userbuf);
if (tmp < 0)
return tmp;
buflen -= tsz;
@@ -225,6 +250,55 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
return acc;
}

+static ssize_t read_vmcore(struct file *file, char __user *buffer,
+ size_t buflen, loff_t *fpos)
+{
+ return __read_vmcore(buffer, buflen, fpos, 1);
+}
+
+/*
+ * The vmcore fault handler uses the page cache and fills data using the
+ * standard __vmcore_read() function.
+ *
+ * On s390 the fault handler is used for memory regions that can't be mapped
+ * directly with remap_pfn_range().
+ */
+static int mmap_vmcore_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+#ifdef CONFIG_S390
+ struct address_space *mapping = vma->vm_file->f_mapping;
+ pgoff_t index = vmf->pgoff;
+ struct page *page;
+ loff_t offset;
+ char *buf;
+ int rc;
+
+ page = find_or_create_page(mapping, index, GFP_KERNEL);
+ if (!page)
+ return VM_FAULT_OOM;
+ if (!PageUptodate(page)) {
+ offset = (loff_t) index << PAGE_CACHE_SHIFT;
+ buf = __va((page_to_pfn(page) << PAGE_SHIFT));
+ rc = __read_vmcore(buf, PAGE_SIZE, &offset, 0);
+ if (rc < 0) {
+ unlock_page(page);
+ page_cache_release(page);
+ return (rc == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS;
+ }
+ SetPageUptodate(page);
+ }
+ unlock_page(page);
+ vmf->page = page;
+ return 0;
+#else
+ return VM_FAULT_SIGBUS;
+#endif
+}
+
+static const struct vm_operations_struct vmcore_mmap_ops = {
+ .fault = mmap_vmcore_fault,
+};
+
/**
* alloc_elfnotes_buf - allocate buffer for ELF note segment in
* vmalloc memory
@@ -271,6 +345,7 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)

vma->vm_flags &= ~(VM_MAYWRITE | VM_MAYEXEC);
vma->vm_flags |= VM_MIXEDMAP;
+ vma->vm_ops = &vmcore_mmap_ops;

len = 0;

@@ -312,9 +387,9 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)

tsz = min_t(size_t, m->offset + m->size - start, size);
paddr = m->paddr + start - m->offset;
- if (remap_pfn_range(vma, vma->vm_start + len,
- paddr >> PAGE_SHIFT, tsz,
- vma->vm_page_prot))
+ if (remap_oldmem_pfn_range(vma, vma->vm_start + len,
+ paddr >> PAGE_SHIFT, tsz,
+ vma->vm_page_prot))
goto fail;
size -= tsz;
start += tsz;
diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
index 6571f82..fe68a5a 100644
--- a/include/linux/crash_dump.h
+++ b/include/linux/crash_dump.h
@@ -17,6 +17,9 @@ extern int __weak elfcorehdr_alloc(unsigned long long *addr,
extern void __weak elfcorehdr_free(unsigned long long addr);
extern ssize_t __weak elfcorehdr_read(char *buf, size_t count, u64 *ppos);
extern ssize_t __weak elfcorehdr_read_notes(char *buf, size_t count, u64 *ppos);
+extern int __weak 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);
--
1.8.2.3


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