[PATCH v6 1/6] system/physmem: handle hugetlb correctly in qemu_ram_remap()

“William Roche
2025-01-27T21:31:39Z

From: William Roche <william.roche@oracle.com>

The list of hwpoison pages used to remap the memory on reset
is based on the backend real page size.
To correctly handle hugetlb, we must mmap(MAP_FIXED) a complete
hugetlb page; hugetlb pages cannot be partially mapped.

Co-developed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: William Roche <william.roche@oracle.com>
---
accel/kvm/kvm-all.c | 2 +-
include/exec/cpu-common.h | 2 +-
system/physmem.c | 38 +++++++++++++++++++++++++++++---------
3 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index c65b790433..f89568bfa3 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -1288,7 +1288,7 @@ static void kvm_unpoison_all(void *param)

QLIST_FOREACH_SAFE(page, &hwpoison_page_list, list, next_page) {
QLIST_REMOVE(page, list);
- qemu_ram_remap(page->ram_addr, TARGET_PAGE_SIZE);
+ qemu_ram_remap(page->ram_addr);
g_free(page);
}
}
diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index b1d76d6985..3771b2130c 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -67,7 +67,7 @@ typedef uintptr_t ram_addr_t;

/* memory API */

-void qemu_ram_remap(ram_addr_t addr, ram_addr_t length);
+void qemu_ram_remap(ram_addr_t addr);
/* This should not be used by devices. */
ram_addr_t qemu_ram_addr_from_host(void *ptr);
ram_addr_t qemu_ram_addr_from_host_nofail(void *ptr);
diff --git a/system/physmem.c b/system/physmem.c
index c76503aea8..3dd2adde73 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2167,17 +2167,35 @@ void qemu_ram_free(RAMBlock *block)
}

#ifndef _WIN32
-void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
+/*
+ * qemu_ram_remap - remap a single RAM page
+ *
+ * @addr: address in ram_addr_t address space.
+ *
+ * This function will try remapping a single page of guest RAM identified by
+ * @addr, essentially discarding memory to recover from previously poisoned
+ * memory (MCE). The page size depends on the RAMBlock (i.e., hugetlb). @addr
+ * does not have to point at the start of the page.
+ *
+ * This function is only to be used during system resets; it will kill the
+ * VM if remapping failed.
+ */
+void qemu_ram_remap(ram_addr_t addr)
{
RAMBlock *block;
- ram_addr_t offset;
+ uint64_t offset;
int flags;
void *area, *vaddr;
int prot;
+ size_t page_size;

RAMBLOCK_FOREACH(block) {
offset = addr - block->offset;
if (offset < block->max_length) {
+ /* Respect the pagesize of our RAMBlock */
+ page_size = qemu_ram_pagesize(block);
+ offset = QEMU_ALIGN_DOWN(offset, page_size);
+
vaddr = ramblock_ptr(block, offset);
if (block->flags & RAM_PREALLOC) {
;
@@ -2191,21 +2209,23 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
prot = PROT_READ;
prot |= block->flags & RAM_READONLY ? 0 : PROT_WRITE;
if (block->fd >= 0) {
- area = mmap(vaddr, length, prot, flags, block->fd,
+ area = mmap(vaddr, page_size, prot, flags, block->fd,
offset + block->fd_offset);
} else {
flags |= MAP_ANONYMOUS;
- area = mmap(vaddr, length, prot, flags, -1, 0);
+ area = mmap(vaddr, page_size, prot, flags, -1, 0);
}
if (area != vaddr) {
- error_report("Could not remap addr: "
- RAM_ADDR_FMT "@" RAM_ADDR_FMT "",
- length, addr);
+ error_report("Could not remap RAM %s:%" PRIx64 "+%" PRIx64
+ " +%zx", block->idstr, offset,
+ block->fd_offset, page_size);
exit(1);
}
- memory_try_enable_merging(vaddr, length);
- qemu_ram_setup_dump(vaddr, length);
+ memory_try_enable_merging(vaddr, page_size);
+ qemu_ram_setup_dump(vaddr, page_size);
}
+
+ break;
}
}
}
--
2.43.5