fs/proc/vmcore: introduce PROC_VMCORE_DEVICE_RAM to detect device RAM ranges in 2nd kernel

s390 allocates+prepares the elfcore hdr in the dump (2nd) kernel, not in
the crashed kernel.

RAM provided by memory devices such as virtio-mem can only be detected
using the device driver; when vmcore_init() is called, these device
drivers are usually not loaded yet, or the devices did not get probed
yet. Consequently, on s390 these RAM ranges will not be included in
the crash dump, which makes the dump partially corrupt and is
unfortunate.

Instead of deferring the vmcore_init() call, to an (unclear?) later point,
let's reuse the vmcore_cb infrastructure to obtain device RAM ranges as
the device drivers probe the device and get access to this information.

Then, we'll add these ranges to the vmcore, adding more PT_LOAD
entries and updating the offsets+vmcore size.

Use a separate Kconfig option to be set by an architecture to include this
code only if the arch really needs it. Further, we'll make the config
depend on the relevant drivers (i.e., virtio_mem) once they implement
support (next). The alternative of having a PROVIDE_PROC_VMCORE_DEVICE_RAM
config option was dropped for now for simplicity.

The current target use case is s390, which only creates an elf64
elfcore, so focusing on elf64 is sufficient.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20241204125444.1734652-9-david@redhat.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
index 5d61c7454fd6..2f2555e6407c 100644
--- a/include/linux/crash_dump.h
+++ b/include/linux/crash_dump.h
@@ -20,6 +20,8 @@ extern int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size);
 extern void elfcorehdr_free(unsigned long long addr);
 extern ssize_t elfcorehdr_read(char *buf, size_t count, u64 *ppos);
 extern ssize_t elfcorehdr_read_notes(char *buf, size_t count, u64 *ppos);
+void elfcorehdr_fill_device_ram_ptload_elf64(Elf64_Phdr *phdr,
+		unsigned long long paddr, unsigned long long size);
 extern int remap_oldmem_pfn_range(struct vm_area_struct *vma,
 				  unsigned long from, unsigned long pfn,
 				  unsigned long size, pgprot_t prot);
@@ -99,6 +101,12 @@ static inline void vmcore_unusable(void)
  *              indicated in the vmcore instead. For example, a ballooned page
  *              contains no data and reading from such a page will cause high
  *              load in the hypervisor.
+ * @get_device_ram: query RAM ranges that can only be detected by device
+ *   drivers, such as the virtio-mem driver, so they can be included in
+ *   the crash dump on architectures that allocate the elfcore hdr in the dump
+ *   ("2nd") kernel. Indicated RAM ranges may contain holes to reduce the
+ *   total number of ranges; such holes can be detected using the pfn_is_ram
+ *   callback just like for other RAM.
  * @next: List head to manage registered callbacks internally; initialized by
  *        register_vmcore_cb().
  *
@@ -109,6 +117,7 @@ static inline void vmcore_unusable(void)
  */
 struct vmcore_cb {
 	bool (*pfn_is_ram)(struct vmcore_cb *cb, unsigned long pfn);
+	int (*get_device_ram)(struct vmcore_cb *cb, struct list_head *list);
 	struct list_head next;
 };
 extern void register_vmcore_cb(struct vmcore_cb *cb);