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

David Hildenbrand
2023-11-15T18:10:42Z

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@intel.com>
> ---
> 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 ? ;)

This should be factored out into a common helper.

--
Cheers,

David / dhildenb