Re: [PATCH v2 1/2] KVM: Refactor kvm_arch_vcpu_fault() to return a struct page pointer
From: Christian Borntraeger
Date: Mon Aug 23 2021 - 10:14:25 EST
On 12.08.21 11:04, David Hildenbrand wrote:
On 12.08.21 06:02, Hou Wenlong wrote:
From: Sean Christopherson <seanjc@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Hou Wenlong <houwenlong93@xxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx>
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.