linux-kernel - Re: [PATCH 07/11] KVM: guest_memfd: extract __kvm_gmem_get

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Date: Tue, 9 Apr 2024 18:35:42 -0500
From: Michael Roth <michael.roth@....com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<seanjc@...gle.com>, <isaku.yamahata@...el.com>
Subject: Re: [PATCH 07/11] KVM: guest_memfd: extract __kvm_gmem_get_pfn()

On Thu, Apr 04, 2024 at 02:50:29PM -0400, Paolo Bonzini wrote:
> In preparation for adding a function that walks a set of pages
> provided by userspace and populates them in a guest_memfd,
> add a version of kvm_gmem_get_pfn() that has a "bool prepare"
> argument and passes it down to kvm_gmem_get_folio().
> 
> Populating guest memory has to call repeatedly __kvm_gmem_get_pfn()
> on the same file, so make the new function take struct file*.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  virt/kvm/guest_memfd.c | 38 +++++++++++++++++++++++---------------
>  1 file changed, 23 insertions(+), 15 deletions(-)
> 
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 486748e65f36..a537a7e63ab5 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -540,33 +540,29 @@ void kvm_gmem_unbind(struct kvm_memory_slot *slot)
>  	fput(file);
>  }
>  
> -int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> -		     gfn_t gfn, kvm_pfn_t *pfn, int *max_order)
> +static int __kvm_gmem_get_pfn(struct file *file, struct kvm_memory_slot *slot,
> +		       gfn_t gfn, kvm_pfn_t *pfn, int *max_order, bool prepare)
>  {
>  	pgoff_t index = gfn - slot->base_gfn + slot->gmem.pgoff;
> -	struct kvm_gmem *gmem;
> +	struct kvm_gmem *gmem = file->private_data;
>  	struct folio *folio;
>  	struct page *page;
> -	struct file *file;
>  	int r;
>  
> -	file = kvm_gmem_get_file(slot);
> -	if (!file)
> +	if (file != slot->gmem.file) {
> +		WARN_ON_ONCE(slot->gmem.file);
>  		return -EFAULT;
> +	}
>  
>  	gmem = file->private_data;
> -
>  	if (xa_load(&gmem->bindings, index) != slot) {
>  		WARN_ON_ONCE(xa_load(&gmem->bindings, index));
> -		r = -EIO;
> -		goto out_fput;
> +		return -EIO;
>  	}
>  
>  	folio = kvm_gmem_get_folio(file_inode(file), index, true);

This should be:

  folio = kvm_gmem_get_folio(file_inode(file), index, prepare);

Otherwise:

Reviewed-by: Michael Roth <michael.roth@....com>

-Mike

> -	if (!folio) {
> -		r = -ENOMEM;
> -		goto out_fput;
> -	}
> +	if (!folio)
> +		return -ENOMEM;
>  
>  	if (folio_test_hwpoison(folio)) {
>  		r = -EHWPOISON;
> @@ -583,9 +579,21 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
>  
>  out_unlock:
>  	folio_unlock(folio);
> -out_fput:
> -	fput(file);
>  
>  	return r;
>  }
> +
> +int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> +		     gfn_t gfn, kvm_pfn_t *pfn, int *max_order)
> +{
> +	struct file *file = kvm_gmem_get_file(slot);
> +	int r;
> +
> +	if (!file)
> +		return -EFAULT;
> +
> +	r = __kvm_gmem_get_pfn(file, slot, gfn, pfn, max_order, true);
> +	fput(file);
> +	return r;
> +}
>  EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
> -- 
> 2.43.0
> 
>