Re: [PATCH v12 05/84] KVM: Add kvm_release_page_unused() API to put pages that KVM never consumes

Alex Bennée
2024-08-01T09:21:21Z

Sean Christopherson <seanjc@google.com> writes:

> Add an API to release an unused page, i.e. to put a page without marking
> it accessed or dirty. The API will be used when KVM faults-in a page but
> bails before installing the guest mapping (and other similar flows).
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> include/linux/kvm_host.h | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 3d9617d1de41..c5d39a337aa3 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1201,6 +1201,15 @@ unsigned long gfn_to_hva_prot(struct kvm *kvm, gfn_t gfn, bool *writable);
> unsigned long gfn_to_hva_memslot(struct kvm_memory_slot *slot, gfn_t gfn);
> unsigned long gfn_to_hva_memslot_prot(struct kvm_memory_slot *slot, gfn_t gfn,
> bool *writable);
> +
> +static inline void kvm_release_page_unused(struct page *page)
> +{
> + if (!page)
> + return;
> +
> + put_page(page);
> +}

I guess it's unfamiliarity with the mm layout but I was trying to find
where the get_pages come from to see the full pattern of allocate and
return. I guess somewhere in the depths of hva_to_pfn() from
hva_to_pfn_retry()? I think the indirection of the page walking confuses
me ;-)

Anyway the API seems reasonable enough given the other kvm_release_
functions.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

--
Alex Bennée
Virtualisation Tech Lead @ Linaro