linux-kernel - Re: [RFC PATCH v2 04/51] KVM: guest_memfd: Introduce KVM_GMEM_CONVERT

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Message-ID: <6825ff323cc63_337c39294e3@iweiny-mobl.notmuch>
Date: Thu, 15 May 2025 09:50:26 -0500
From: Ira Weiny <ira.weiny@...el.com>
To: Ackerley Tng <ackerleytng@...gle.com>, <kvm@...r.kernel.org>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	<linux-fsdevel@...r.kernel.org>
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Subject: Re: [RFC PATCH v2 04/51] KVM: guest_memfd: Introduce
 KVM_GMEM_CONVERT_SHARED/PRIVATE ioctls

Ackerley Tng wrote:

[snip]

> Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
> 

[snip]

> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 590932499eba..f802116290ce 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -30,6 +30,10 @@ enum shareability {
>  };
>  
>  static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index);
> +static void kvm_gmem_invalidate_begin(struct kvm_gmem *gmem, pgoff_t start,
> +				      pgoff_t end);
> +static void kvm_gmem_invalidate_end(struct kvm_gmem *gmem, pgoff_t start,
> +				    pgoff_t end);
>  
>  static struct kvm_gmem_inode_private *kvm_gmem_private(struct inode *inode)
>  {
> @@ -85,6 +89,306 @@ static struct folio *kvm_gmem_get_shared_folio(struct inode *inode, pgoff_t inde
>  	return kvm_gmem_get_folio(inode, index);
>  }
>  
> +/**
> + * kvm_gmem_shareability_store() - Sets shareability to @value for range.
> + *
> + * @mt: the shareability maple tree.
> + * @index: the range begins at this index in the inode.
> + * @nr_pages: number of PAGE_SIZE pages in this range.
> + * @value: the shareability value to set for this range.
> + *
> + * Unlike mtree_store_range(), this function also merges adjacent ranges that
> + * have the same values as an optimization.

Is this an optimization or something which will be required to convert
from shared back to private and back to a huge page mapping?

If this is purely an optimization it might be best to leave it out for now
to get functionality first.

I have more to review but wanted to ask this.

Ira

[snip]