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Date: Mon, 23 Aug 2021 16:12:40 +0200
From: Christian Borntraeger <borntraeger@...ibm.com>
To: David Hildenbrand <david@...hat.com>,
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>,
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 11:04, David Hildenbrand wrote:
> 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.
I recently talked to the ucontrol users and they will look into selftests.
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