On 02/02/2025 06:52, Gavin Shan wrote:
> On 12/13/24 1:55 AM, Steven Price wrote:
>> Always split up huge pages to avoid problems managing huge pages. There
>> are two issues currently:
>>
>> 1. The uABI for the VMM allows populating memory on 4k boundaries even
>> if the underlying allocator (e.g. hugetlbfs) is using a larger page
>> size. Using a memfd for private allocations will push this issue onto
>> the VMM as it will need to respect the granularity of the allocator.
>>
>> 2. The guest is able to request arbitrary ranges to be remapped as
>> shared. Again with a memfd approach it will be up to the VMM to deal
>> with the complexity and either overmap (need the huge mapping and add
>> an additional 'overlapping' shared mapping) or reject the request as
>> invalid due to the use of a huge page allocator.
>>
>> For now just break everything down to 4k pages in the RMM controlled
>> stage 2.
>>
>> Signed-off-by: Steven Price <steven.price@xxxxxxx>
>> ---
>> 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 e88714903ce5..9ede143ccef1 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -1603,6 +1603,10 @@ static int user_mem_abort(struct kvm_vcpu
>> *vcpu, phys_addr_t fault_ipa,
>> if (logging_active) {
>> force_pte = true;
>> vma_shift = PAGE_SHIFT;
>> + } else if (kvm_is_realm(kvm)) {
>> + // Force PTE level mappings for realms
>> + force_pte = true;
>> + vma_shift = PAGE_SHIFT;
>> } else {
>> vma_shift = get_vma_page_shift(vma, hva);
>> }
>
> Since a memory abort is specific to a vCPU instead of a VM, so
> vcpu_is_rec()
> instead of kvm_is_realm() is more accurate for the check. Besides, it looks
> duplicate to the check added by "PATCH[20/43] arm64: RME: Runtime faulting
> of memory", which is as below.
>
> /* FIXME: We shouldn't need to disable this for realms */
> if (vma_pagesize == PAGE_SIZE && !(force_pte || device ||
> kvm_is_realm(kvm))) {
>
> ^^^^^^^^^^^^^^^^^
> Can be
> dropped now.
Indeed, thanks for that - one less FIXME ;)
Thanks,
Steve
> Thanks,
> Gavin
>
>
