[v2,2/7] system/physmem: poisoned memory discard on reboot

Commit Message

“William Roche Nov. 7, 2024, 10:21 a.m. UTC

From: William Roche <[e-mail]>

We take into account the recorded page sizes to repair the
memory locations, calling ram_block_discard_range() to punch a hole
in the backend file when necessary and regenerate a usable memory.
Fall back to unmap/remap the memory location(s) if the kernel doesn't
support the madvise calls used by ram_block_discard_range().

Hugetlbfs poison case is also taken into account as a hole punch
with fallocate will reload a new page when first touched.

Signed-off-by: William Roche <[e-mail]>
---
 system/physmem.c | 50 +++++++++++++++++++++++++++++-------------------
 1 file changed, 30 insertions(+), 20 deletions(-)

Patch

diff --git a/system/physmem.c b/system/physmem.c
index 750604d47d..dfea120cc5 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2197,27 +2197,37 @@  void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
             } else if (xen_enabled()) {
                 abort();
             } else {
-                flags = MAP_FIXED;
-                flags |= block->flags & RAM_SHARED ?
-                         MAP_SHARED : MAP_PRIVATE;
-                flags |= block->flags & RAM_NORESERVE ? MAP_NORESERVE : 0;
-                prot = PROT_READ;
-                prot |= block->flags & RAM_READONLY ? 0 : PROT_WRITE;
-                if (block->fd >= 0) {
-                    area = mmap(vaddr, length, prot, flags, block->fd,
-                                offset + block->fd_offset);
-                } else {
-                    flags |= MAP_ANONYMOUS;
-                    area = mmap(vaddr, length, prot, flags, -1, 0);
-                }
-                if (area != vaddr) {
-                    error_report("Could not remap addr: "
-                                 RAM_ADDR_FMT "@" RAM_ADDR_FMT "",
-                                 length, addr);
-                    exit(1);
+                if (ram_block_discard_range(block, offset + block->fd_offset,
+                                            length) != 0) {
+                    if (length > TARGET_PAGE_SIZE) {
+                        /* punch hole is mandatory on hugetlbfs */
+                        error_report("large page recovery failure addr: "
+                                     RAM_ADDR_FMT "@" RAM_ADDR_FMT "",
+                                     length, addr);
+                        exit(1);
+                    }
+                    flags = MAP_FIXED;
+                    flags |= block->flags & RAM_SHARED ?
+                             MAP_SHARED : MAP_PRIVATE;
+                    flags |= block->flags & RAM_NORESERVE ? MAP_NORESERVE : 0;
+                    prot = PROT_READ;
+                    prot |= block->flags & RAM_READONLY ? 0 : PROT_WRITE;
+                    if (block->fd >= 0) {
+                        area = mmap(vaddr, length, prot, flags, block->fd,
+                                    offset + block->fd_offset);
+                    } else {
+                        flags |= MAP_ANONYMOUS;
+                        area = mmap(vaddr, length, prot, flags, -1, 0);
+                    }
+                    if (area != vaddr) {
+                        error_report("Could not remap addr: "
+                                     RAM_ADDR_FMT "@" RAM_ADDR_FMT "",
+                                     length, addr);
+                        exit(1);
+                    }
+                    memory_try_enable_merging(vaddr, length);
+                    qemu_ram_setup_dump(vaddr, length);
                 }
-                memory_try_enable_merging(vaddr, length);
-                qemu_ram_setup_dump(vaddr, length);
             }
         }
     }