linux-kernel - Re: [PATCH v7 1/9] KVM: arm/arm64: Ensure only THP is candidate for adjustment

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Date:   Mon, 24 Sep 2018 21:54:02 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Punit Agrawal <punit.agrawal@....com>, kvmarm@...ts.cs.columbia.edu
Cc:     marc.zyngier@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Christoffer Dall <christoffer.dall@....com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v7 1/9] KVM: arm/arm64: Ensure only THP is candidate for
 adjustment

Hi Punit,

On 09/24/2018 06:45 PM, Punit Agrawal wrote:
> PageTransCompoundMap() returns true for hugetlbfs and THP
> hugepages. This behaviour incorrectly leads to stage 2 faults for
> unsupported hugepage sizes (e.g., 64K hugepage with 4K pages) to be
> treated as THP faults.
> 
> Tighten the check to filter out hugetlbfs pages. This also leads to
> consistently mapping all unsupported hugepage sizes as PTE level
> entries at stage 2.
> 
> Signed-off-by: Punit Agrawal <punit.agrawal@....com>
> Cc: Christoffer Dall <christoffer.dall@....com>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Suzuki Poulose <suzuki.poulose@....com>
> Cc: stable@...r.kernel.org # v4.13+
> ---
>   virt/kvm/arm/mmu.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 7e477b3cae5b..c23a1b323aad 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -1231,8 +1231,14 @@ static bool transparent_hugepage_adjust(kvm_pfn_t *pfnp, phys_addr_t *ipap)
>   {
>   	kvm_pfn_t pfn = *pfnp;
>   	gfn_t gfn = *ipap >> PAGE_SHIFT;
> +	struct page *page = pfn_to_page(pfn);
>   
> -	if (PageTransCompoundMap(pfn_to_page(pfn))) {
> +	/*
> +	 * PageTransCompoungMap() returns true for THP and
> +	 * hugetlbfs. Make sure the adjustment is done only for THP
> +	 * pages.
> +	 */
> +	if (!PageHuge(page) && PageTransCompoundMap(page)) {

Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>