linux-kernel - Re: [PATCH v17 16/24] KVM: x86/mmu: Handle guest page faults for guest

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Message-ID: <cf196e44-4ec1-45ab-9cd4-dd8cb10bd44f@intel.com>
Date: Wed, 30 Jul 2025 15:37:31 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
 Oliver Upton <oliver.upton@...ux.dev>
Cc: kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Ira Weiny <ira.weiny@...el.com>, Gavin Shan <gshan@...hat.com>,
 Shivank Garg <shivankg@....com>, Vlastimil Babka <vbabka@...e.cz>,
 David Hildenbrand <david@...hat.com>, Fuad Tabba <tabba@...gle.com>,
 Ackerley Tng <ackerleytng@...gle.com>, Tao Chan <chentao@...inos.cn>,
 James Houghton <jthoughton@...gle.com>
Subject: Re: [PATCH v17 16/24] KVM: x86/mmu: Handle guest page faults for
 guest_memfd with shared memory

On 7/30/2025 6:54 AM, Sean Christopherson wrote:
> From: Ackerley Tng <ackerleytng@...gle.com>
> 
> Update the KVM MMU fault handler to service guest page faults
> for memory slots backed by guest_memfd with mmap support. For such
> slots, the MMU must always fault in pages directly from guest_memfd,
> bypassing the host's userspace_addr.
> 
> This ensures that guest_memfd-backed memory is always handled through
> the guest_memfd specific faulting path, regardless of whether it's for
> private or non-private (shared) use cases.
> 
> Additionally, rename kvm_mmu_faultin_pfn_private() to
> kvm_mmu_faultin_pfn_gmem(), as this function is now used to fault in
> pages from guest_memfd for both private and non-private memory,
> accommodating the new use cases.
> 
> Co-developed-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
> Co-developed-by: Fuad Tabba <tabba@...gle.com>
> Signed-off-by: Fuad Tabba <tabba@...gle.com>
> [sean: drop the helper]
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>

> ---
>   arch/x86/kvm/mmu/mmu.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e83d666f32ad..56c80588efa0 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4561,8 +4561,8 @@ static void kvm_mmu_finish_page_fault(struct kvm_vcpu *vcpu,
>   				 r == RET_PF_RETRY, fault->map_writable);
>   }
>   
> -static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu,
> -				       struct kvm_page_fault *fault)
> +static int kvm_mmu_faultin_pfn_gmem(struct kvm_vcpu *vcpu,
> +				    struct kvm_page_fault *fault)
>   {
>   	int max_order, r;
>   
> @@ -4589,8 +4589,8 @@ static int __kvm_mmu_faultin_pfn(struct kvm_vcpu *vcpu,
>   {
>   	unsigned int foll = fault->write ? FOLL_WRITE : 0;
>   
> -	if (fault->is_private)
> -		return kvm_mmu_faultin_pfn_private(vcpu, fault);
> +	if (fault->is_private || kvm_memslot_is_gmem_only(fault->slot))
> +		return kvm_mmu_faultin_pfn_gmem(vcpu, fault);
>   
>   	foll |= FOLL_NOWAIT;
>   	fault->pfn = __kvm_faultin_pfn(fault->slot, fault->gfn, foll,