linux-kernel - Re: [PATCH v12 01/84] KVM: arm64: Release pfn, i.e. put page, if copying MTE tags hits ZONE

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Message-ID: <ZrOBg70pCnv7PHyK@arm.com>
Date: Wed, 7 Aug 2024 15:15:31 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>,
	Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Anup Patel <anup@...infault.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Janosch Frank <frankja@...ux.ibm.com>,
	Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	David Matlack <dmatlack@...gle.com>,
	David Stevens <stevensd@...omium.org>,
	Steven Price <steven.price@....com>
Subject: Re: [PATCH v12 01/84] KVM: arm64: Release pfn, i.e. put page, if
 copying MTE tags hits ZONE_DEVICE

On Fri, Jul 26, 2024 at 04:51:10PM -0700, Sean Christopherson wrote:
> Put the page reference acquired by gfn_to_pfn_prot() if
> kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory.  KVM's less-
> than-stellar heuristics for dealing with pfn-mapped memory means that KVM
> can get a page reference to ZONE_DEVICE memory.
> 
> Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/arm64/kvm/guest.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 11098eb7eb44..e1f0ff08836a 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -1059,6 +1059,7 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
>  		page = pfn_to_online_page(pfn);
>  		if (!page) {
>  			/* Reject ZONE_DEVICE memory */
> +			kvm_release_pfn_clean(pfn);
>  			ret = -EFAULT;
>  			goto out;
>  		}

This patch makes sense irrespective of whether the above pfn is a
ZONE_DEVICE or not. gfn_to_pfn_prot() increased the page refcount via
GUP, so it must be released before bailing out of this loop.

Reviewed-by: Catalin Marinas <catalin.marinas@....com>