Re: [PATCH 3/5] KVM: Remove kvm_is_transparent_hugepage() and PageTransCompoundMap()

[Paolo Bonzini <pbonzini@redhat.com>]

On 17/07/21 11:55, Marc Zyngier wrote:
> Now that arm64 has stopped using kvm_is_transparent_hugepage(),
> we can remove it, as well as PageTransCompoundMap() which was
> only used by the former.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>   include/linux/page-flags.h | 37 -------------------------------------
>   virt/kvm/kvm_main.c        | 10 ----------
>   2 files changed, 47 deletions(-)
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 5922031ffab6..1ace27c4a8e0 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -632,43 +632,6 @@ static inline int PageTransCompound(struct page *page)
>   	return PageCompound(page);
>   }
>   
> -/*
> - * PageTransCompoundMap is the same as PageTransCompound, but it also
> - * guarantees the primary MMU has the entire compound page mapped
> - * through pmd_trans_huge, which in turn guarantees the secondary MMUs
> - * can also map the entire compound page. This allows the secondary
> - * MMUs to call get_user_pages() only once for each compound page and
> - * to immediately map the entire compound page with a single secondary
> - * MMU fault. If there will be a pmd split later, the secondary MMUs
> - * will get an update through the MMU notifier invalidation through
> - * split_huge_pmd().
> - *
> - * Unlike PageTransCompound, this is safe to be called only while
> - * split_huge_pmd() cannot run from under us, like if protected by the
> - * MMU notifier, otherwise it may result in page->_mapcount check false
> - * positives.
> - *
> - * We have to treat page cache THP differently since every subpage of it
> - * would get _mapcount inc'ed once it is PMD mapped.  But, it may be PTE
> - * mapped in the current process so comparing subpage's _mapcount to
> - * compound_mapcount to filter out PTE mapped case.
> - */
> -static inline int PageTransCompoundMap(struct page *page)
> -{
> -	struct page *head;
> -
> -	if (!PageTransCompound(page))
> -		return 0;
> -
> -	if (PageAnon(page))
> -		return atomic_read(&page->_mapcount) < 0;
> -
> -	head = compound_head(page);
> -	/* File THP is PMD mapped and not PTE mapped */
> -	return atomic_read(&page->_mapcount) ==
> -	       atomic_read(compound_mapcount_ptr(head));
> -}
> -
>   /*
>    * PageTransTail returns true for both transparent huge pages
>    * and hugetlbfs pages, so it should only be called when it's known
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 7d95126cda9e..2e410a8a6a67 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -189,16 +189,6 @@ bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
>   	return true;
>   }
>   
> -bool kvm_is_transparent_hugepage(kvm_pfn_t pfn)
> -{
> -	struct page *page = pfn_to_page(pfn);
> -
> -	if (!PageTransCompoundMap(page))
> -		return false;
> -
> -	return is_transparent_hugepage(compound_head(page));
> -}
> -
>   /*
>    * Switches to specified vcpu, until a matching vcpu_put()
>    */
> 

Acked-by: Paolo Bonzini <pbonzini@redhat.com>