Re: [PATCH v1 3/4] system/physmem: Largepage punch hole before reset of memory pages

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On 22.10.24 23:35, “William Roche wrote:
From: William Roche <william.roche@xxxxxxxxxx>

When the VM reboots, a memory reset is performed calling
qemu_ram_remap() on all hwpoisoned pages.
While we take into account the recorded page sizes to repair the
memory locations, a large page also needs to punch a hole in the
backend file to regenerate a usable memory, cleaning the HW
poisoned section. This is mandatory for hugetlbfs case for example.

Signed-off-by: William Roche <william.roche@xxxxxxxxxx>
---
  system/physmem.c | 8 ++++++++
  1 file changed, 8 insertions(+)

diff --git a/system/physmem.c b/system/physmem.c
index 3757428336..3f6024a92d 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2211,6 +2211,14 @@ 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 {

Ah! Just what I commented to patch #3; we should be using ram_discard_range(). It might be better to avoid the mmap() completely if ram_discard_range() worked.

And as raised, there is the problem with memory preallocation (where we should fail if it doesn't work) and ram discards being disabled because something relies on long-term page pinning ...

--
Cheers,

David / dhildenb





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