Re: [PATCH v2 1/2] ram-block-attributes: Avoid the overkill of shared memory with hugetlbfs backend

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 10/23/2025 5:55 PM, Chenyi Qiang wrote:
> Currently, CoCo VMs can perform conversion at the base page granularity,
> which is the granularity that has to be tracked. In relevant setups, the
> target page size is assumed to be equal to the host page size, thus
> fixing the block size to the host page size.
> 
> However, since private memory and shared memory have different backend
> at present, users can specify shared memory with a hugetlbfs backend
> while private memory with guest_memfd backend only supports 4K page
> size. In this scenario, ram_block->page_size is different from the host
> page size which will trigger an assertion when retrieving the block
> size.
> 
> To address this, return the host page size directly to relax the
> restriction. This changes fixes a regression of using hugetlbfs backend
> for shared memory within CoCo VMs, with or without VFIO devices' presence.
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> Tested-by: Farrah Chen <farrah.chen@intel.com>
> Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>

The change looks good to me.

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>

> ---
> Changes in v2:
>    - Modify the commit message
>    - Remove the argument in ram_block_attributes_get_block_size()
> ---
>   system/ram-block-attributes.c | 18 ++++++++----------
>   1 file changed, 8 insertions(+), 10 deletions(-)
> 
> diff --git a/system/ram-block-attributes.c b/system/ram-block-attributes.c
> index 68e8a027032..a7579de5b46 100644
> --- a/system/ram-block-attributes.c
> +++ b/system/ram-block-attributes.c
> @@ -22,16 +22,14 @@ OBJECT_DEFINE_SIMPLE_TYPE_WITH_INTERFACES(RamBlockAttributes,
>                                             { })
>   
>   static size_t
> -ram_block_attributes_get_block_size(const RamBlockAttributes *attr)
> +ram_block_attributes_get_block_size(void)
>   {
>       /*
>        * Because page conversion could be manipulated in the size of at least 4K
>        * or 4K aligned, Use the host page size as the granularity to track the
>        * memory attribute.
>        */
> -    g_assert(attr && attr->ram_block);
> -    g_assert(attr->ram_block->page_size == qemu_real_host_page_size());
> -    return attr->ram_block->page_size;
> +    return qemu_real_host_page_size();
>   }
>   
>   
> @@ -40,7 +38,7 @@ ram_block_attributes_rdm_is_populated(const RamDiscardManager *rdm,
>                                         const MemoryRegionSection *section)
>   {
>       const RamBlockAttributes *attr = RAM_BLOCK_ATTRIBUTES(rdm);
> -    const size_t block_size = ram_block_attributes_get_block_size(attr);
> +    const size_t block_size = ram_block_attributes_get_block_size();
>       const uint64_t first_bit = section->offset_within_region / block_size;
>       const uint64_t last_bit =
>           first_bit + int128_get64(section->size) / block_size - 1;
> @@ -81,7 +79,7 @@ ram_block_attributes_for_each_populated_section(const RamBlockAttributes *attr,
>   {
>       unsigned long first_bit, last_bit;
>       uint64_t offset, size;
> -    const size_t block_size = ram_block_attributes_get_block_size(attr);
> +    const size_t block_size = ram_block_attributes_get_block_size();
>       int ret = 0;
>   
>       first_bit = section->offset_within_region / block_size;
> @@ -122,7 +120,7 @@ ram_block_attributes_for_each_discarded_section(const RamBlockAttributes *attr,
>   {
>       unsigned long first_bit, last_bit;
>       uint64_t offset, size;
> -    const size_t block_size = ram_block_attributes_get_block_size(attr);
> +    const size_t block_size = ram_block_attributes_get_block_size();
>       int ret = 0;
>   
>       first_bit = section->offset_within_region / block_size;
> @@ -163,7 +161,7 @@ ram_block_attributes_rdm_get_min_granularity(const RamDiscardManager *rdm,
>       const RamBlockAttributes *attr = RAM_BLOCK_ATTRIBUTES(rdm);
>   
>       g_assert(mr == attr->ram_block->mr);
> -    return ram_block_attributes_get_block_size(attr);
> +    return ram_block_attributes_get_block_size();
>   }
>   
>   static void
> @@ -265,7 +263,7 @@ ram_block_attributes_is_valid_range(RamBlockAttributes *attr, uint64_t offset,
>       g_assert(mr);
>   
>       uint64_t region_size = memory_region_size(mr);
> -    const size_t block_size = ram_block_attributes_get_block_size(attr);
> +    const size_t block_size = ram_block_attributes_get_block_size();
>   
>       if (!QEMU_IS_ALIGNED(offset, block_size) ||
>           !QEMU_IS_ALIGNED(size, block_size)) {
> @@ -322,7 +320,7 @@ int ram_block_attributes_state_change(RamBlockAttributes *attr,
>                                         uint64_t offset, uint64_t size,
>                                         bool to_discard)
>   {
> -    const size_t block_size = ram_block_attributes_get_block_size(attr);
> +    const size_t block_size = ram_block_attributes_get_block_size();
>       const unsigned long first_bit = offset / block_size;
>       const unsigned long nbits = size / block_size;
>       const unsigned long last_bit = first_bit + nbits - 1;