[RFC RESEND 3/6] system/physmem: Remap memory pages on reset based on the page size

["“William Roche" <william.roche@oracle.com>]

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

When the VM reboots, a memory reset is performed calling
qemu_ram_remap() on all hwpoisoned pages.
We take into account the recorded page size to adjust the
size and location of the memory hole.
In case of a largepage used, we also need to punch a hole
in the backend file to regenerate a usable memory, cleaning
the HW poisoned section.

Signed-off-by: William Roche <william.roche@oracle.com>
---
 system/physmem.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/system/physmem.c b/system/physmem.c
index 94600a33ec..5c176146c0 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2195,6 +2195,11 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
     RAMBLOCK_FOREACH(block) {
         offset = addr - block->offset;
         if (offset < block->max_length) {
+            /* addr could be a subpage of a former large page */
+            if (length < block->page_size) {
+                offset = ROUND_DOWN(offset, block->page_size);
+                length = block->page_size;
+            }
             vaddr = ramblock_ptr(block, offset);
             if (block->flags & RAM_PREALLOC) {
                 ;
@@ -2208,6 +2213,14 @@ 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) {
+                    if (length > TARGET_PAGE_SIZE && fallocate(block->fd,
+                        FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
+                        offset + block->fd_offset, length) != 0) {
+                        error_report("Could not recreate the file hole for "
+                                     "addr: " RAM_ADDR_FMT "@" RAM_ADDR_FMT "",
+                                     length, addr);
+                        exit(1);
+                    }
                     area = mmap(vaddr, length, prot, flags, block->fd,
                                 offset + block->fd_offset);
                 } else {
-- 
2.43.5