linux-kernel - Re: [PATCH v12 50/84] KVM: VMX: Use __kvm_faultin

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <bb2d52e8-ceff-46e8-83a1-4db535754aa0@redhat.com>
Date: Tue, 30 Jul 2024 10:59:57 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.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>
Cc: 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>
Subject: Re: [PATCH v12 50/84] KVM: VMX: Use __kvm_faultin_page() to get APIC
 access page/pfn

On 7/27/24 01:51, Sean Christopherson wrote:
> Use __kvm_faultin_page() get the APIC access page so that KVM can
> precisely release the refcounted page, i.e. to remove yet another user
> of kvm_pfn_to_refcounted_page().  While the path isn't handling a guest
> page fault, the semantics are effectively the same; KVM just happens to
> be mapping the pfn into a VMCS field instead of a secondary MMU.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/vmx/vmx.c | 13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 30032585f7dc..b109bd282a52 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6786,8 +6786,10 @@ void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
>   	struct kvm *kvm = vcpu->kvm;
>   	struct kvm_memslots *slots = kvm_memslots(kvm);
>   	struct kvm_memory_slot *slot;
> +	struct page *refcounted_page;
>   	unsigned long mmu_seq;
>   	kvm_pfn_t pfn;
> +	bool ign;

Even if you don't use it, call the out argument "writable".

Paolo

>   
>   	/* Defer reload until vmcs01 is the current VMCS. */
>   	if (is_guest_mode(vcpu)) {
> @@ -6823,7 +6825,7 @@ void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
>   	 * controls the APIC-access page memslot, and only deletes the memslot
>   	 * if APICv is permanently inhibited, i.e. the memslot won't reappear.
>   	 */
> -	pfn = gfn_to_pfn_memslot(slot, gfn);
> +	pfn = __kvm_faultin_pfn(slot, gfn, FOLL_WRITE, &ign, &refcounted_page);
>   	if (is_error_noslot_pfn(pfn))
>   		return;
>   
> @@ -6834,10 +6836,13 @@ void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
>   		vmcs_write64(APIC_ACCESS_ADDR, pfn_to_hpa(pfn));
>   
>   	/*
> -	 * Do not pin apic access page in memory, the MMU notifier
> -	 * will call us again if it is migrated or swapped out.
> +	 * Do not pin the APIC access page in memory so that it can be freely
> +	 * migrated, the MMU notifier will call us again if it is migrated or
> +	 * swapped out.  KVM backs the memslot with anonymous memory, the pfn
> +	 * should always point at a refcounted page (if the pfn is valid).
>   	 */
> -	kvm_release_pfn_clean(pfn);
> +	if (!WARN_ON_ONCE(!refcounted_page))
> +		kvm_release_page_clean(refcounted_page);
>   
>   	/*
>   	 * No need for a manual TLB flush at this point, KVM has already done a