Yeah, I ignored that fact as well. So essentially, this patch should be
mostly good for now.
From here [1], these changes will make it to v9
+ kvm_max_private_mapping_level renaming to kvm_max_gmem_mapping_level
+ kvm_mmu_faultin_pfn_private renaming to kvm_mmu_faultin_pfn_gmem
Only kvm_mmu_hugepage_adjust() must be taught to not rely on
fault->is_private.
I think fault->is_private should contribute to determining the max
mapping level.
By the time kvm_mmu_hugepage_adjust() is called,
* For Coco VMs using guest_memfd only for private memory,
* fault->is_private would have been checked to align with
kvm->mem_attr_array, so
* For Coco VMs using guest_memfd for both private/shared memory,
* fault->is_private would have been checked to align with
guest_memfd's shareability
* For non-Coco VMs using guest_memfd
* fault->is_private would be false
But as Sean said, looking at the code might be easier.
Maybe just send the resulting diff of the patch here real quick?
Hence fault->is_private can be relied on when calling
kvm_mmu_hugepage_adjust().
If fault->is_private, there will be no host userspace mapping to check,
hence in __kvm_mmu_max_mapping_level(), we should skip querying host
page tables.
If !fault->is_private, for shared memory ranges, if the VM uses
guest_memfd only for shared memory, we should query host page tables.
If !fault->is_private, for shared memory ranges, if the VM uses
guest_memfd for both shared/private memory, we should not query host
page tables.
> > If !fault->is_private, for non-Coco VMs, we should not query host page
tables.
> > I propose to rename the parameter is_private to skip_host_page_tables,
so
- if (is_private)
+ if (skip_host_page_tables)
return max_level;
and pass
skip_host_page_tables = fault->is_private ||
kvm_gmem_memslot_supports_shared(fault->slot);
How is that better than calling it "is_gmem" / "from_gmem" etc? :)
Anyhow, no strong opinion, spelling out that something is from gmem
implies that we don't care about page tables.
where kvm_gmem_memslot_supports_shared() checks the inode in the memslot
for GUEST_MEMFD_FLAG_SUPPORT_SHARED.
Makes sense.
--
Cheers,
David / dhildenb
