linux-kernel - Re: [RFC PATCH v1 06/37] KVM: guest_memfd: Update kvm_gmem

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Message-ID: <diqzzf8oazh4.fsf@google.com>
Date: Fri, 14 Nov 2025 16:52:55 -0800
From: Ackerley Tng <ackerleytng@...gle.com>
To: Yan Zhao <yan.y.zhao@...el.com>
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Subject: Re: [RFC PATCH v1 06/37] KVM: guest_memfd: Update kvm_gmem_populate()
 to use gmem attributes

Yan Zhao <yan.y.zhao@...el.com> writes:

>>  #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE
>> +static bool kvm_gmem_range_is_private(struct gmem_inode *gi, pgoff_t index,
>> +				      size_t nr_pages, struct kvm *kvm, gfn_t gfn)
>> +{
>> +	pgoff_t end = index + nr_pages - 1;
>> +	void *entry;
>> +
>> +	if (vm_memory_attributes)
>> +		return kvm_range_has_vm_memory_attributes(kvm, gfn, gfn + nr_pages,
>> +						       KVM_MEMORY_ATTRIBUTE_PRIVATE,
>> +						       KVM_MEMORY_ATTRIBUTE_PRIVATE);
> Can't compile kvm_range_has_vm_memory_attributes() if
> CONFIG_KVM_VM_MEMORY_ATTRIBUTES is not set.

Thanks! I will fix this in the next revision.


We've been discussing HugeTLB support in the guest_memfd upstream calls
and I'd like to add a quick follow up here, with code, for anyone who
might be interested. Here's a WIP tree:

https://github.com/googleprodkernel/linux-cc/tree/wip-gmem-conversions-hugetlb-restructuring

This tree was based off kvm-next (as of 2025-10-08), and includes

+ Mmap fixes from Sean
+ NUMA mempolicy support from Shivank Garg (AMD)
+ Some cleanup patches from Sean
+ Conversion series [1] with some cleanups (Thanks for the comments and
  reviews on this series! Haven't had time to figure out all of it,
  addressed some first)
+ st_blocks fix for guest_memfd, which was discussed at the guest_memfd
  upstream call: slides [2]
+ HugeTLB support without conversion: this stage does not yet take into
  account comments from the upstream call. This stage provides support
  for HugeTLB to be used through guest_memfd for private memory. This
  has to be used with the KVM parameter vm_memory_attributes set to
  true. This stage can be used to test Yan's TDX huge page support by
  setting up guest_memfd with HugeTLB just for private memory, with
  shared memory being taken from elsewhere.
+ HugeTLB support with conversion and folio restructuring: this stage
  also does not take into account comments from the upstream call, so it
  still disables the INIT_SHARED flag, although HugeTLB can now be used
  with in-place conversion for both shared and private memory. This can
  be used to test Yan's TDX huge page support.

[1] https://lore.kernel.org/all/cover.1760731772.git.ackerleytng@google.com/T/
[2] https://lpc.events/event/18/contributions/1764/attachments/1409/3715/2025-10-30%20guest_memfd%20upstream%20call_%20guest_memfd%20HugeTLB%20support%20overview.pdf