From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Date: Mon, 23 Aug 2021 14:12:40 +0000 Subject: Re: [PATCH v2 1/2] KVM: Refactor kvm_arch_vcpu_fault() to return a struct page pointer Message-Id: List-Id: References: <1c510b24fc1d7cbae8aa4b69c0799ebd32e65b82.1628739116.git.houwenlong93@linux.alibaba.com> <98adbd3c-ec6f-5689-1686-2a8a7909951a@redhat.com> In-Reply-To: <98adbd3c-ec6f-5689-1686-2a8a7909951a@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: David Hildenbrand , Hou Wenlong , kvm@vger.kernel.org Cc: x86@kernel.org, Wanpeng Li , Benjamin Herrenschmidt , linux-mips@vger.kernel.org, Paul Mackerras , "H. Peter Anvin" , Claudio Imbrenda , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-s390@vger.kernel.org, Janosch Frank , Marc Zyngier , Joerg Roedel , Huacai Chen , Aleksandar Markovic , Ingo Molnar , Catalin Marinas , Vasily Gorbik , Heiko Carstens , kvm-ppc@vger.kernel.org, Borislav Petkov , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Jim Mattson , Thomas Bogendoerfer , Sean Christopherson , Cornelia Huck , linux-kernel@vger.kernel.org, Michael Ellerman , Paolo Bonzini , Vitaly Kuznetsov , linuxppc-dev@lists.ozlabs.org On 12.08.21 11:04, David Hildenbrand wrote: > On 12.08.21 06:02, Hou Wenlong wrote: >> From: Sean Christopherson >> >> 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 >> Signed-off-by: Sean Christopherson >> Signed-off-by: Hou Wenlong >> --- >>   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 > > 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.