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Message-ID: <98adbd3c-ec6f-5689-1686-2a8a7909951a@redhat.com>
Date: Thu, 12 Aug 2021 11:04:58 +0200
From: David Hildenbrand <david@...hat.com>
To: Hou Wenlong <houwenlong93@...ux.alibaba.com>, kvm@...r.kernel.org
Cc: Sean Christopherson <seanjc@...gle.com>,
Marc Zyngier <maz@...nel.org>,
James Morse <james.morse@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Huacai Chen <chenhuacai@...nel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
Paul Mackerras <paulus@...abs.org>,
Michael Ellerman <mpe@...erman.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Christian Borntraeger <borntraeger@...ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
Cornelia Huck <cohuck@...hat.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
kvm-ppc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
linux-s390@...r.kernel.org
Subject: Re: [PATCH v2 1/2] KVM: Refactor kvm_arch_vcpu_fault() to return a
struct page pointer
On 12.08.21 06:02, Hou Wenlong wrote:
> From: Sean Christopherson <seanjc@...gle.com>
>
> Refactor kvm_arch_vcpu_fault() to return 'struct page *' instead of
> 'vm_fault_t' to simplify architecture specific implementations that do
> more than return SIGBUS. Currently this only applies to s390, but a
> future patch will move x86's pio_data handling into x86 where it belongs.
>
> No functional changed intended.
>
> Cc: Hou Wenlong <houwenlong93@...ux.alibaba.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Hou Wenlong <houwenlong93@...ux.alibaba.com>
> ---
> arch/arm64/kvm/arm.c | 4 ++--
> arch/mips/kvm/mips.c | 4 ++--
> arch/powerpc/kvm/powerpc.c | 4 ++--
> arch/s390/kvm/kvm-s390.c | 12 ++++--------
> arch/x86/kvm/x86.c | 4 ++--
> include/linux/kvm_host.h | 2 +-
> virt/kvm/kvm_main.c | 5 ++++-
> 7 files changed, 17 insertions(+), 18 deletions(-)
>
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index e9a2b8f27792..83f4ffe3e4f2 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -161,9 +161,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> return ret;
> }
>
> -vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> +struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> {
> - return VM_FAULT_SIGBUS;
> + return NULL;
> }
>
>
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index af9dd029a4e1..ae79874e6fd2 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -1053,9 +1053,9 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
> return -ENOIOCTLCMD;
> }
>
> -vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> +struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> {
> - return VM_FAULT_SIGBUS;
> + return NULL;
> }
>
> int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index be33b5321a76..b9c21f9ab784 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -2090,9 +2090,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> return r;
> }
>
> -vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> +struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> {
> - return VM_FAULT_SIGBUS;
> + return NULL;
> }
>
> static int kvm_vm_ioctl_get_pvinfo(struct kvm_ppc_pvinfo *pvinfo)
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 02574d7b3612..e1b69833e228 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -4979,17 +4979,13 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> return r;
> }
>
> -vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> +struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> {
> #ifdef CONFIG_KVM_S390_UCONTROL
> - if ((vmf->pgoff == KVM_S390_SIE_PAGE_OFFSET)
> - && (kvm_is_ucontrol(vcpu->kvm))) {
> - vmf->page = virt_to_page(vcpu->arch.sie_block);
> - get_page(vmf->page);
> - return 0;
> - }
> + if (vmf->pgoff == KVM_S390_SIE_PAGE_OFFSET && kvm_is_ucontrol(vcpu->kvm))
> + return virt_to_page(vcpu->arch.sie_block);
> #endif
> - return VM_FAULT_SIGBUS;
> + return NULL;
> }
>
> /* Section: memory related */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 3cedc7cc132a..1e3bbe5cd33a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5347,9 +5347,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> return r;
> }
>
> -vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> +struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> {
> - return VM_FAULT_SIGBUS;
> + return NULL;
> }
>
> static int kvm_vm_ioctl_set_tss_addr(struct kvm *kvm, unsigned long addr)
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 492d183dd7d0..a949de534722 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -995,7 +995,7 @@ long kvm_arch_dev_ioctl(struct file *filp,
> unsigned int ioctl, unsigned long arg);
> long kvm_arch_vcpu_ioctl(struct file *filp,
> unsigned int ioctl, unsigned long arg);
> -vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf);
> +struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf);
>
> int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext);
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 30d322519253..f7d21418971b 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3448,7 +3448,10 @@ static vm_fault_t kvm_vcpu_fault(struct vm_fault *vmf)
> &vcpu->dirty_ring,
> vmf->pgoff - KVM_DIRTY_LOG_PAGE_OFFSET);
> else
> - return kvm_arch_vcpu_fault(vcpu, vmf);
> + page = kvm_arch_vcpu_fault(vcpu, vmf);
> + if (!page)
> + return VM_FAULT_SIGBUS;
> +
> get_page(page);
> vmf->page = page;
> return 0;
>
Reviewed-by: David Hildenbrand <david@...hat.com>
But at the same time I wonder if we should just get rid of
CONFIG_KVM_S390_UCONTROL and consequently kvm_arch_vcpu_fault().
In practice CONFIG_KVM_S390_UCONTROL, is never enabled in any reasonable
kernel build and consequently it's never tested; further, exposing the
sie_block to user space allows user space to generate random SIE
validity intercepts.
CONFIG_KVM_S390_UCONTROL feels like something that should just be
maintained out of tree by someone who really needs to hack deep into hw
virtualization for testing purposes etc.
--
Thanks,
David / dhildenb
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