Re: [PATCH v3 03/70] RAMBlock/guest_memfd: Enable KVM_GUEST_MEMFD_ALLOW_HUGEPAGE

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On 11/16/2023 2:10 AM, David Hildenbrand wrote:
On 15.11.23 08:14, Xiaoyao Li wrote:
KVM allows KVM_GUEST_MEMFD_ALLOW_HUGEPAGE for guest memfd. When the
flag is set, KVM tries to allocate memory with transparent hugeapge at
first and falls back to non-hugepage on failure.

However, KVM defines one restriction that size must be hugepage size
aligned when KVM_GUEST_MEMFD_ALLOW_HUGEPAGE is set.

Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
---
v3:
  - New one in v3.
---
  system/physmem.c | 38 ++++++++++++++++++++++++++++++++++++--
  1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/system/physmem.c b/system/physmem.c
index 0af2213cbd9c..c56b17e44df6 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -1803,6 +1803,40 @@ static void dirty_memory_extend(ram_addr_t old_ram_size,
      }
  }
+#ifdef CONFIG_KVM
+#define HPAGE_PMD_SIZE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
+#define DEFAULT_PMD_SIZE (1ul << 21)
+
+static uint32_t get_thp_size(void)
+{
+    gchar *content = NULL;
+    const char *endptr;
+    static uint64_t thp_size = 0;
+    uint64_t tmp;
+
+    if (thp_size != 0) {
+        return thp_size;
+    }
+
+    if (g_file_get_contents(HPAGE_PMD_SIZE_PATH, &content, NULL, NULL) &&
+        !qemu_strtou64(content, &endptr, 0, &tmp) &&
+        (!endptr || *endptr == '\n')) {
+        /* Sanity-check the value and fallback to something reasonable. */
+        if (!tmp || !is_power_of_2(tmp)) {
+            warn_report("Read unsupported THP size: %" PRIx64, tmp);
+        } else {
+            thp_size = tmp;
+        }
+    }
+
+    if (!thp_size) {
+        thp_size = DEFAULT_PMD_SIZE;
+    }

... did you shamelessly copy that from hw/virtio/virtio-mem.c ? ;)

Get caught.

This should be factored out into a common helper.

Sure, will do it in next version.





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