[PATCH] KVM: Use vma_lookup() in kvm_host_page_size()

[PATCH] KVM: Use vma_lookup() in kvm_host_page_size()

[David Woodhouse]

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From: David Woodhouse <dwmw@amazon.co.uk>

kvm_host_page_size() uses find_vma() to determine the host page size
backing a guest page. find_vma() returns the next VMA when the address
falls in an unmapped hole, which means an unmapped address inherits the
page size of a completely unrelated VMA at a higher address. This is
never a meaningful result.

Replace find_vma() with vma_lookup() so that a hole address returns
NULL, causing the function to return PAGE_SIZE (the safe default)
rather than an unrelated VMA's page size.

This is currently only cosmetic, as the only caller is in PPC book3s
support (kvmppc_xive_native_set_queue_config()) and subsequently returns
failure if !gfn_to_page() anyway.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 89489996fbc1..d33761123459 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2693,7 +2693,7 @@ unsigned long kvm_host_page_size(struct kvm_vcpu *vcpu, gfn_t gfn)
 		return PAGE_SIZE;
 
 	mmap_read_lock(current->mm);
-	vma = find_vma(current->mm, addr);
+	vma = vma_lookup(current->mm, addr);
 	if (!vma)
 		goto out;
 
-- 
2.43.0


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Re: [PATCH] KVM: Use vma_lookup() in kvm_host_page_size()

[Ritesh Harjani]

David Woodhouse <dwmw2@infradead.org> writes:

> From: David Woodhouse <dwmw@amazon.co.uk>
>
> kvm_host_page_size() uses find_vma() to determine the host page size
> backing a guest page. find_vma() returns the next VMA when the address
> falls in an unmapped hole, which means an unmapped address inherits the
> page size of a completely unrelated VMA at a higher address. This is
> never a meaningful result.
>
> Replace find_vma() with vma_lookup() so that a hole address returns
> NULL, causing the function to return PAGE_SIZE (the safe default)
> rather than an unrelated VMA's page size.
>

That's exactly right.

> This is currently only cosmetic, as the only caller is in PPC book3s
> support (kvmppc_xive_native_set_queue_config()) and subsequently returns
> failure if !gfn_to_page() anyway.
>

Yup. The change make sense to me. Feel free to add:
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>


> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>  virt/kvm/kvm_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 89489996fbc1..d33761123459 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2693,7 +2693,7 @@ unsigned long kvm_host_page_size(struct kvm_vcpu *vcpu, gfn_t gfn)
>  		return PAGE_SIZE;
>  
>  	mmap_read_lock(current->mm);
> -	vma = find_vma(current->mm, addr);
> +	vma = vma_lookup(current->mm, addr);
>  	if (!vma)
>  		goto out;
>  
> -- 
> 2.43.0