On 16/04/2025 14:41, Steven Price wrote:
> Guest_memfd doesn't yet natively support huge pages, and there are
> currently difficulties for a VMM to manage huge pages efficiently so for
> now always split up mappings to PTE (4k).
>
> The two issues that need progressing before supporting huge pages for
> realms are:
>
> 1. guest_memfd needs to be able to allocate from an appropriate
> allocator which can provide huge pages.
>
> 2. The VMM needs to be able to repurpose private memory for a shared
> mapping when the guest VM requests memory is transitioned. Because
> this can happen at a 4k granularity it isn't possible to
> free/reallocate while huge pages are in use. Allowing the VMM to
> mmap() the shared portion of a huge page would allow the huge page
> to be recreated when the memory is unshared and made protected again.
>
> These two issues are not specific to realms and don't affect the realm
> API, so for now just break everything down to 4k pages in the RMM
> controlled stage 2. Future work can add huge page support without
> changing the uAPI.
>
> Signed-off-by: Steven Price <steven.price@arm.com>
With comments from Gavin addressed,
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
> Changes since v7:
> * Rewritten commit message
> ---
> arch/arm64/kvm/mmu.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 02b66ee35426..29bab7a46033 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1653,6 +1653,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> if (logging_active || is_protected_kvm_enabled()) {
> force_pte = true;
> vma_shift = PAGE_SHIFT;
> + } else if (vcpu_is_rec(vcpu)) {
> + // Force PTE level mappings for realms
> + force_pte = true;
> + vma_shift = PAGE_SHIFT;
> } else {
> vma_shift = get_vma_page_shift(vma, hva);
> }