Re: [PATCH v2 4/6] kexec_file: Add mechanism to update kexec segments.

[Thiago Jung Bauermann]

Hello Andrew,

Thank you for your review!

Am Montag, 15 August 2016, 15:27:56 schrieb Andrew Morton:
> On Sat, 13 Aug 2016 00:18:23 -0300 Thiago Jung Bauermann 
> <bauer...@linux.vnet.ibm.com> wrote:
> > +/**
> > + * kexec_update_segment - update the contents of a kimage segment
> > + * @buffer:New contents of the segment.
> > + * @bufsz: @buffer size.
> > + * @load_addr: Segment's physical address in the next kernel.
> > + * @memsz: Segment size.
> > + *
> > + * This function assumes kexec_mutex is held.
> > + *
> > + * Return: 0 on success, negative errno on error.
> > + */
> > +int kexec_update_segment(const char *buffer, unsigned long bufsz,
> > +unsigned long load_addr, unsigned long memsz)
> > +{
> > +   int i;
> > +   unsigned long entry;
> > +   unsigned long *ptr = NULL;
> > +   void *dest = NULL;
> > +
> > +   if (kexec_image == NULL) {
> > +   pr_err("Can't update segment: no kexec image loaded.\n");
> > +   return -EINVAL;
> > +   }
> > +
> > +   /*
> > +* kexec_add_buffer rounds up segment sizes to PAGE_SIZE, so
> > +* we have to do it here as well.
> > +*/
> > +   memsz = ALIGN(memsz, PAGE_SIZE);
> > +
> > +   for (i = 0; i < kexec_image->nr_segments; i++)
> > +   /* We only support updating whole segments. */
> > +   if (load_addr == kexec_image->segment[i].mem &&
> > +   memsz == kexec_image->segment[i].memsz) {
> > +   if (kexec_image->segment[i].do_checksum) {
> > +   pr_err("Trying to update non-modifiable 
> > segment.\n");
> > +   return -EINVAL;
> > +   }
> > +
> > +   break;
> > +   }
> > +   if (i == kexec_image->nr_segments) {
> > +   pr_err("Couldn't find segment to update: 0x%lx, size 0x%lx\n",
> > +  load_addr, memsz);
> > +   return -EINVAL;
> > +   }
> > +
> > +   for (entry = kexec_image->head; !(entry & IND_DONE) && memsz;
> > +entry = *ptr++) {
> > +   void *addr = (void *) (entry & PAGE_MASK);
> > +
> > +   switch (entry & IND_FLAGS) {
> > +   case IND_DESTINATION:
> > +   dest = addr;
> > +   break;
> > +   case IND_INDIRECTION:
> > +   ptr = __va(addr);
> > +   break;
> > +   case IND_SOURCE:
> > +   /* Shouldn't happen, but verify just to be safe. */
> > +   if (dest == NULL) {
> > +   pr_err("Invalid kexec entries list.");
> > +   return -EINVAL;
> > +   }
> > +
> > +   if (dest == (void *) load_addr) {
> > +   struct page *page;
> > +   char *ptr;
> > +   size_t uchunk, mchunk;
> > +
> > +   page = kmap_to_page(addr);
> > +
> > +   ptr = kmap(page);
> 
> kmap_atomic() could be used here, and it is appreciably faster.

Good idea. The patch below implements your suggestion.

This has a consequence for patch 5/6 in this series, because it makes
this code be used in the path of the kexec_file_load and
kexec_load syscalls.

In the latter case, there's a call to copy_from_user and thus kmap_atomic 
can't be used. I can change the patch to use kmap_atomic if
state->from_kernel is true and kmap otherwise, but perhaps this is one more 
hint that patch 5/6 is not a very good idea after all.

-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center


Subject: [PATCH v2 4/6] kexec_file: Add mechanism to update kexec segments.

kexec_update_segment allows a given segment in kexec_image to have
its contents updated. This is useful if the current kernel wants to
send information to the next kernel that is up-to-date at the time of
reboot.

Signed-off-by: Thiago Jung Bauermann <bauer...@linux.vnet.ibm.com>
---
 include/linux/kexec.h |  2 ++
 kernel/kexec_core.c   | 99 +++
 2 files changed, 101 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 37eea32fdff1..14dda81e3e01 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -259,6 +259,8 @@ extern int kexec_purgatory_get_set_symbol(struct kimage 
*image,
  unsigned int size, bool get_value);
 ext

Re: [PATCH v2 4/6] kexec_file: Add mechanism to update kexec segments.

[Andrew Morton]

On Sat, 13 Aug 2016 00:18:23 -0300 Thiago Jung Bauermann 
 wrote:

> kexec_update_segment allows a given segment in kexec_image to have
> its contents updated. This is useful if the current kernel wants to
> send information to the next kernel that is up-to-date at the time of
> reboot.
> 
> ...
>
> @@ -721,6 +721,105 @@ static struct page *kimage_alloc_page(struct kimage 
> *image,
>   return page;
>  }
>  
> +/**
> + * kexec_update_segment - update the contents of a kimage segment
> + * @buffer:  New contents of the segment.
> + * @bufsz:   @buffer size.
> + * @load_addr:   Segment's physical address in the next kernel.
> + * @memsz:   Segment size.
> + *
> + * This function assumes kexec_mutex is held.
> + *
> + * Return: 0 on success, negative errno on error.
> + */
> +int kexec_update_segment(const char *buffer, unsigned long bufsz,
> +  unsigned long load_addr, unsigned long memsz)
> +{
> + int i;
> + unsigned long entry;
> + unsigned long *ptr = NULL;
> + void *dest = NULL;
> +
> + if (kexec_image == NULL) {
> + pr_err("Can't update segment: no kexec image loaded.\n");
> + return -EINVAL;
> + }
> +
> + /*
> +  * kexec_add_buffer rounds up segment sizes to PAGE_SIZE, so
> +  * we have to do it here as well.
> +  */
> + memsz = ALIGN(memsz, PAGE_SIZE);
> +
> + for (i = 0; i < kexec_image->nr_segments; i++)
> + /* We only support updating whole segments. */
> + if (load_addr == kexec_image->segment[i].mem &&
> + memsz == kexec_image->segment[i].memsz) {
> + if (kexec_image->segment[i].do_checksum) {
> + pr_err("Trying to update non-modifiable 
> segment.\n");
> + return -EINVAL;
> + }
> +
> + break;
> + }
> + if (i == kexec_image->nr_segments) {
> + pr_err("Couldn't find segment to update: 0x%lx, size 0x%lx\n",
> +load_addr, memsz);
> + return -EINVAL;
> + }
> +
> + for (entry = kexec_image->head; !(entry & IND_DONE) && memsz;
> +  entry = *ptr++) {
> + void *addr = (void *) (entry & PAGE_MASK);
> +
> + switch (entry & IND_FLAGS) {
> + case IND_DESTINATION:
> + dest = addr;
> + break;
> + case IND_INDIRECTION:
> + ptr = __va(addr);
> + break;
> + case IND_SOURCE:
> + /* Shouldn't happen, but verify just to be safe. */
> + if (dest == NULL) {
> + pr_err("Invalid kexec entries list.");
> + return -EINVAL;
> + }
> +
> + if (dest == (void *) load_addr) {
> + struct page *page;
> + char *ptr;
> + size_t uchunk, mchunk;
> +
> + page = kmap_to_page(addr);
> +
> + ptr = kmap(page);

kmap_atomic() could be used here, and it is appreciably faster.


> + ptr += load_addr & ~PAGE_MASK;
> + mchunk = min_t(size_t, memsz,
> +PAGE_SIZE - (load_addr & 
> ~PAGE_MASK));
> + uchunk = min(bufsz, mchunk);
> + memcpy(ptr, buffer, uchunk);
> +
> + kunmap(page);
> +
> + bufsz -= uchunk;
> + load_addr += mchunk;
> + buffer += mchunk;
> + memsz -= mchunk;
> + }
> + dest += PAGE_SIZE;
> + }
> +
> + /* Shouldn't happen, but verify just to be safe. */
> + if (ptr == NULL) {
> + pr_err("Invalid kexec entries list.");
> + return -EINVAL;
> + }
> + }
> +
> + return 0;
> +}
> +


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[PATCH v2 4/6] kexec_file: Add mechanism to update kexec segments.

[Thiago Jung Bauermann]

kexec_update_segment allows a given segment in kexec_image to have
its contents updated. This is useful if the current kernel wants to
send information to the next kernel that is up-to-date at the time of
reboot.

Signed-off-by: Thiago Jung Bauermann 
---
 include/linux/kexec.h |  2 ++
 kernel/kexec_core.c   | 99 +++
 2 files changed, 101 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 37eea32fdff1..14dda81e3e01 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -259,6 +259,8 @@ extern int kexec_purgatory_get_set_symbol(struct kimage 
*image,
  unsigned int size, bool get_value);
 extern void *kexec_purgatory_get_symbol_addr(struct kimage *image,
 const char *name);
+int kexec_update_segment(const char *buffer, unsigned long bufsz,
+unsigned long load_addr, unsigned long memsz);
 extern void __crash_kexec(struct pt_regs *);
 extern void crash_kexec(struct pt_regs *);
 int kexec_should_crash(struct task_struct *);
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 561675589511..806735201de6 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -721,6 +721,105 @@ static struct page *kimage_alloc_page(struct kimage 
*image,
return page;
 }
 
+/**
+ * kexec_update_segment - update the contents of a kimage segment
+ * @buffer:New contents of the segment.
+ * @bufsz: @buffer size.
+ * @load_addr: Segment's physical address in the next kernel.
+ * @memsz: Segment size.
+ *
+ * This function assumes kexec_mutex is held.
+ *
+ * Return: 0 on success, negative errno on error.
+ */
+int kexec_update_segment(const char *buffer, unsigned long bufsz,
+unsigned long load_addr, unsigned long memsz)
+{
+   int i;
+   unsigned long entry;
+   unsigned long *ptr = NULL;
+   void *dest = NULL;
+
+   if (kexec_image == NULL) {
+   pr_err("Can't update segment: no kexec image loaded.\n");
+   return -EINVAL;
+   }
+
+   /*
+* kexec_add_buffer rounds up segment sizes to PAGE_SIZE, so
+* we have to do it here as well.
+*/
+   memsz = ALIGN(memsz, PAGE_SIZE);
+
+   for (i = 0; i < kexec_image->nr_segments; i++)
+   /* We only support updating whole segments. */
+   if (load_addr == kexec_image->segment[i].mem &&
+   memsz == kexec_image->segment[i].memsz) {
+   if (kexec_image->segment[i].do_checksum) {
+   pr_err("Trying to update non-modifiable 
segment.\n");
+   return -EINVAL;
+   }
+
+   break;
+   }
+   if (i == kexec_image->nr_segments) {
+   pr_err("Couldn't find segment to update: 0x%lx, size 0x%lx\n",
+  load_addr, memsz);
+   return -EINVAL;
+   }
+
+   for (entry = kexec_image->head; !(entry & IND_DONE) && memsz;
+entry = *ptr++) {
+   void *addr = (void *) (entry & PAGE_MASK);
+
+   switch (entry & IND_FLAGS) {
+   case IND_DESTINATION:
+   dest = addr;
+   break;
+   case IND_INDIRECTION:
+   ptr = __va(addr);
+   break;
+   case IND_SOURCE:
+   /* Shouldn't happen, but verify just to be safe. */
+   if (dest == NULL) {
+   pr_err("Invalid kexec entries list.");
+   return -EINVAL;
+   }
+
+   if (dest == (void *) load_addr) {
+   struct page *page;
+   char *ptr;
+   size_t uchunk, mchunk;
+
+   page = kmap_to_page(addr);
+
+   ptr = kmap(page);
+   ptr += load_addr & ~PAGE_MASK;
+   mchunk = min_t(size_t, memsz,
+  PAGE_SIZE - (load_addr & 
~PAGE_MASK));
+   uchunk = min(bufsz, mchunk);
+   memcpy(ptr, buffer, uchunk);
+
+   kunmap(page);
+
+   bufsz -= uchunk;
+   load_addr += mchunk;
+   buffer += mchunk;
+   memsz -= mchunk;
+   }
+   dest += PAGE_SIZE;
+   }
+
+   /* Shouldn't happen, but verify just to be safe. */
+   if (ptr == NULL) {
+   pr_err("Invalid kexec entries list.");
+   return