| Message ID | 20220118041923.3384602-1-reijiw@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/2] KVM: arm64: mixed-width check should be skipped for uninitialized vCPUs | expand |
On Tue, 18 Jan 2022 04:19:22 +0000, Reiji Watanabe <reijiw@google.com> wrote: > > KVM allows userspace to configure either all 32bit or 64bit vCPUs > for a guest. At vCPU reset, vcpu_allowed_register_width() checks > if the vcpu's register width is consistent with all other vCPUs'. > Since the checking is done even against vCPUs that are not initialized > (KVM_ARM_VCPU_INIT has not been done) yet, the uninitialized vCPUs > are erroneously treated as 64bit vCPU, which causes the function to > incorrectly detect a mixed-width VM. > > Introduce a new flag (el1_reg_width) in kvm_arch to indicates that > the guest needs to be configured with all 32bit or 64bit vCPUs, > and initialize it at the first KVM_ARM_VCPU_INIT for the guest. > Check vcpu's register width against the flag at the vcpu's > KVM_ARM_VCPU_INIT (instead of against other vCPUs' register width). > > Fixes: 66e94d5cafd4 ("KVM: arm64: Prevent mixed-width VM creation") > Signed-off-by: Reiji Watanabe <reijiw@google.com> > --- > arch/arm64/include/asm/kvm_host.h | 13 +++++++++++++ > arch/arm64/kvm/arm.c | 30 ++++++++++++++++++++++++++++++ > arch/arm64/kvm/reset.c | 8 -------- > 3 files changed, 43 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index 2a5f7f38006f..c02b7caf2c82 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -102,6 +102,12 @@ struct kvm_s2_mmu { > struct kvm_arch_memory_slot { > }; > > +enum kvm_el1_reg_width { > + EL1_WIDTH_UNINITIALIZED = 0, > + EL1_32BIT, > + EL1_64BIT, > +}; > + > struct kvm_arch { > struct kvm_s2_mmu mmu; > > @@ -137,6 +143,13 @@ struct kvm_arch { > > /* Memory Tagging Extension enabled for the guest */ > bool mte_enabled; > + > + /* > + * EL1 register width for the guest. > + * This is set at the first KVM_ARM_VCPU_INIT for the guest based > + * on whether the vcpu has KVM_ARM_VCPU_EL1_32BIT or not. > + */ > + enum kvm_el1_reg_width el1_reg_width; I really don't like that we need to keep track of yet another bit of state on top of the existing one. Duplicating state is a source of bugs, because you always end up checking the wrong one at the wrong time (and I have scars to prove it). > }; > > struct kvm_vcpu_fault_info { > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index e4727dc771bf..54ae8bf9d187 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -1058,6 +1058,32 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level, > return -EINVAL; > } > > +/* > + * A guest can have either all 32bit or 64bit vcpus only. That's not strictly true. All we are enforcing is that EL1 is either 32 or 64bit. > + * Either one the guest has is indicated in kvm->arch.el1_reg_width. > + * Check if the vcpu's register width is consistent with > + * kvm->arch.el1_reg_width. If kvm->arch.el1_reg_width is not set yet, > + * set it based on the vcpu's KVM_ARM_VCPU_EL1_32BIT configuration. > + */ > +static int kvm_register_width_check_or_init(struct kvm_vcpu *vcpu) > +{ > + bool is32bit; > + bool allowed = true; > + struct kvm *kvm = vcpu->kvm; > + > + is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT); > + > + mutex_lock(&kvm->lock); > + > + if (kvm->arch.el1_reg_width == EL1_WIDTH_UNINITIALIZED) > + kvm->arch.el1_reg_width = is32bit ? EL1_32BIT : EL1_64BIT; > + else > + allowed = (is32bit == (kvm->arch.el1_reg_width == EL1_32BIT)); > + > + mutex_unlock(&kvm->lock); > + return allowed ? 0 : -EINVAL; > +} > + > static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu, > const struct kvm_vcpu_init *init) > { > @@ -1097,6 +1123,10 @@ static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu, > > /* Now we know what it is, we can reset it. */ > ret = kvm_reset_vcpu(vcpu); > + > + if (!ret) > + ret = kvm_register_width_check_or_init(vcpu); > + > if (ret) { > vcpu->arch.target = -1; > bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES); > diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c > index 426bd7fbc3fd..dbf2939a6a96 100644 > --- a/arch/arm64/kvm/reset.c > +++ b/arch/arm64/kvm/reset.c > @@ -168,9 +168,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu) > > static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu) > { > - struct kvm_vcpu *tmp; > bool is32bit; > - int i; > > is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT); > if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) && is32bit) > @@ -180,12 +178,6 @@ static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu) > if (kvm_has_mte(vcpu->kvm) && is32bit) > return false; > > - /* Check that the vcpus are either all 32bit or all 64bit */ > - kvm_for_each_vcpu(i, tmp, vcpu->kvm) { > - if (vcpu_has_feature(tmp, KVM_ARM_VCPU_EL1_32BIT) != is32bit) > - return false; > - } > - In [1], I suggested another approach that didn't require extra state, and moved the existing checks under the kvm lock. What was wrong with that approach? Thanks, M. [1] https://lore.kernel.org/r/875yqqtn5q.wl-maz@kernel.org
Hi Marc, On Tue, Feb 8, 2022 at 6:41 AM Marc Zyngier <maz@kernel.org> wrote: > > On Tue, 18 Jan 2022 04:19:22 +0000, > Reiji Watanabe <reijiw@google.com> wrote: > > > > KVM allows userspace to configure either all 32bit or 64bit vCPUs > > for a guest. At vCPU reset, vcpu_allowed_register_width() checks > > if the vcpu's register width is consistent with all other vCPUs'. > > Since the checking is done even against vCPUs that are not initialized > > (KVM_ARM_VCPU_INIT has not been done) yet, the uninitialized vCPUs > > are erroneously treated as 64bit vCPU, which causes the function to > > incorrectly detect a mixed-width VM. > > > > Introduce a new flag (el1_reg_width) in kvm_arch to indicates that > > the guest needs to be configured with all 32bit or 64bit vCPUs, > > and initialize it at the first KVM_ARM_VCPU_INIT for the guest. > > Check vcpu's register width against the flag at the vcpu's > > KVM_ARM_VCPU_INIT (instead of against other vCPUs' register width). > > > > Fixes: 66e94d5cafd4 ("KVM: arm64: Prevent mixed-width VM creation") > > Signed-off-by: Reiji Watanabe <reijiw@google.com> > > --- > > arch/arm64/include/asm/kvm_host.h | 13 +++++++++++++ > > arch/arm64/kvm/arm.c | 30 ++++++++++++++++++++++++++++++ > > arch/arm64/kvm/reset.c | 8 -------- > > 3 files changed, 43 insertions(+), 8 deletions(-) > > > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > > index 2a5f7f38006f..c02b7caf2c82 100644 > > --- a/arch/arm64/include/asm/kvm_host.h > > +++ b/arch/arm64/include/asm/kvm_host.h > > @@ -102,6 +102,12 @@ struct kvm_s2_mmu { > > struct kvm_arch_memory_slot { > > }; > > > > +enum kvm_el1_reg_width { > > + EL1_WIDTH_UNINITIALIZED = 0, > > + EL1_32BIT, > > + EL1_64BIT, > > +}; > > + > > struct kvm_arch { > > struct kvm_s2_mmu mmu; > > > > @@ -137,6 +143,13 @@ struct kvm_arch { > > > > /* Memory Tagging Extension enabled for the guest */ > > bool mte_enabled; > > + > > + /* > > + * EL1 register width for the guest. > > + * This is set at the first KVM_ARM_VCPU_INIT for the guest based > > + * on whether the vcpu has KVM_ARM_VCPU_EL1_32BIT or not. > > + */ > > + enum kvm_el1_reg_width el1_reg_width; > > I really don't like that we need to keep track of yet another bit of > state on top of the existing one. Duplicating state is a source of > bugs, because you always end up checking the wrong one at the wrong > time (and I have scars to prove it). > > > }; > > > > struct kvm_vcpu_fault_info { > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > > index e4727dc771bf..54ae8bf9d187 100644 > > --- a/arch/arm64/kvm/arm.c > > +++ b/arch/arm64/kvm/arm.c > > @@ -1058,6 +1058,32 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level, > > return -EINVAL; > > } > > > > +/* > > + * A guest can have either all 32bit or 64bit vcpus only. > > That's not strictly true. All we are enforcing is that EL1 is either > 32 or 64bit. I will fix the comment. > > > + * Either one the guest has is indicated in kvm->arch.el1_reg_width. > > + * Check if the vcpu's register width is consistent with > > + * kvm->arch.el1_reg_width. If kvm->arch.el1_reg_width is not set yet, > > + * set it based on the vcpu's KVM_ARM_VCPU_EL1_32BIT configuration. > > + */ > > +static int kvm_register_width_check_or_init(struct kvm_vcpu *vcpu) > > +{ > > + bool is32bit; > > + bool allowed = true; > > + struct kvm *kvm = vcpu->kvm; > > + > > + is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT); > > + > > + mutex_lock(&kvm->lock); > > + > > + if (kvm->arch.el1_reg_width == EL1_WIDTH_UNINITIALIZED) > > + kvm->arch.el1_reg_width = is32bit ? EL1_32BIT : EL1_64BIT; > > + else > > + allowed = (is32bit == (kvm->arch.el1_reg_width == EL1_32BIT)); > > + > > + mutex_unlock(&kvm->lock); > > + return allowed ? 0 : -EINVAL; > > +} > > + > > static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu, > > const struct kvm_vcpu_init *init) > > { > > @@ -1097,6 +1123,10 @@ static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu, > > > > /* Now we know what it is, we can reset it. */ > > ret = kvm_reset_vcpu(vcpu); > > + > > + if (!ret) > > + ret = kvm_register_width_check_or_init(vcpu); > > + > > if (ret) { > > vcpu->arch.target = -1; > > bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES); > > diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c > > index 426bd7fbc3fd..dbf2939a6a96 100644 > > --- a/arch/arm64/kvm/reset.c > > +++ b/arch/arm64/kvm/reset.c > > @@ -168,9 +168,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu) > > > > static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu) > > { > > - struct kvm_vcpu *tmp; > > bool is32bit; > > - int i; > > > > is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT); > > if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) && is32bit) > > @@ -180,12 +178,6 @@ static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu) > > if (kvm_has_mte(vcpu->kvm) && is32bit) > > return false; > > > > - /* Check that the vcpus are either all 32bit or all 64bit */ > > - kvm_for_each_vcpu(i, tmp, vcpu->kvm) { > > - if (vcpu_has_feature(tmp, KVM_ARM_VCPU_EL1_32BIT) != is32bit) > > - return false; > > - } > > - > > In [1], I suggested another approach that didn't require extra state, > and moved the existing checks under the kvm lock. What was wrong with > that approach? With that approach, even for a vcpu that has a broken set of features, which leads kvm_reset_vcpu() to fail for the vcpu, the vcpu->arch.features are checked by other vCPUs' vcpu_allowed_register_width() until the vcpu->arch.target is set to -1. Due to this, I would think some or possibly all vCPUs' kvm_reset_vcpu() may or may not fail (e.g. if userspace tries to configure vCPU#0 with 32bit EL1, and vCPU#1 and #2 with 64 bit EL1, KVM_ARM_VCPU_INIT for either vCPU#0, or both vCPU#1 and #2 should fail. But, with that approach, it doesn't always work that way. Instead, KVM_ARM_VCPU_INIT for all vCPUs could fail or KVM_ARM_VCPU_INIT for vCPU#0 and #1 could fail while the one for CPU#2 works). Also, even after the first KVM_RUN for vCPUs are already done, (the first) KVM_ARM_VCPU_INIT for another vCPU could cause the kvm_reset_vcpu() for those vCPUs to fail. I would think those behaviors are odd, and I wanted to avoid them. Thanks, Reiji > > Thanks, > > M. > > [1] https://lore.kernel.org/r/875yqqtn5q.wl-maz@kernel.org > > -- > Without deviation from the norm, progress is not possible.
Hi Reiji, On Wed, 09 Feb 2022 05:32:36 +0000, Reiji Watanabe <reijiw@google.com> wrote: > > Hi Marc, > > On Tue, Feb 8, 2022 at 6:41 AM Marc Zyngier <maz@kernel.org> wrote: > > > > In [1], I suggested another approach that didn't require extra state, > > and moved the existing checks under the kvm lock. What was wrong with > > that approach? > > With that approach, even for a vcpu that has a broken set of features, > which leads kvm_reset_vcpu() to fail for the vcpu, the vcpu->arch.features > are checked by other vCPUs' vcpu_allowed_register_width() until the > vcpu->arch.target is set to -1. > Due to this, I would think some or possibly all vCPUs' kvm_reset_vcpu() > may or may not fail (e.g. if userspace tries to configure vCPU#0 with > 32bit EL1, and vCPU#1 and #2 with 64 bit EL1, KVM_ARM_VCPU_INIT > for either vCPU#0, or both vCPU#1 and #2 should fail. But, with that > approach, it doesn't always work that way. Instead, KVM_ARM_VCPU_INIT > for all vCPUs could fail or KVM_ARM_VCPU_INIT for vCPU#0 and #1 could > fail while the one for CPU#2 works). > Also, even after the first KVM_RUN for vCPUs are already done, > (the first) KVM_ARM_VCPU_INIT for another vCPU could cause the > kvm_reset_vcpu() for those vCPUs to fail. > > I would think those behaviors are odd, and I wanted to avoid them. OK, fair enough. But then you need to remove most of the uses of KVM_ARM_VCPU_EL1_32BIT so that it is only used as a userspace interface and maybe not carried as part of the vcpu feature flag anymore. Also, we really should turn all these various bits in the kvm struct into a set of flags. I have a patch posted there[1] for this, feel free to pick it up. Thanks, M. [1] https://lore.kernel.org/r/20211004174849.2831548-2-maz@kernel.org
Hi Marc, On Wed, Feb 9, 2022 at 4:04 AM Marc Zyngier <maz@kernel.org> wrote: > > Hi Reiji, > > On Wed, 09 Feb 2022 05:32:36 +0000, > Reiji Watanabe <reijiw@google.com> wrote: > > > > Hi Marc, > > > > On Tue, Feb 8, 2022 at 6:41 AM Marc Zyngier <maz@kernel.org> wrote: > > > > > > In [1], I suggested another approach that didn't require extra state, > > > and moved the existing checks under the kvm lock. What was wrong with > > > that approach? > > > > With that approach, even for a vcpu that has a broken set of features, > > which leads kvm_reset_vcpu() to fail for the vcpu, the vcpu->arch.features > > are checked by other vCPUs' vcpu_allowed_register_width() until the > > vcpu->arch.target is set to -1. > > Due to this, I would think some or possibly all vCPUs' kvm_reset_vcpu() > > may or may not fail (e.g. if userspace tries to configure vCPU#0 with > > 32bit EL1, and vCPU#1 and #2 with 64 bit EL1, KVM_ARM_VCPU_INIT > > for either vCPU#0, or both vCPU#1 and #2 should fail. But, with that > > approach, it doesn't always work that way. Instead, KVM_ARM_VCPU_INIT > > for all vCPUs could fail or KVM_ARM_VCPU_INIT for vCPU#0 and #1 could > > fail while the one for CPU#2 works). > > Also, even after the first KVM_RUN for vCPUs are already done, > > (the first) KVM_ARM_VCPU_INIT for another vCPU could cause the > > kvm_reset_vcpu() for those vCPUs to fail. > > > > I would think those behaviors are odd, and I wanted to avoid them. > > OK, fair enough. But then you need to remove most of the uses of > KVM_ARM_VCPU_EL1_32BIT so that it is only used as a userspace > interface and Yes, I will. > maybe not carried as part of the vcpu feature flag anymore. At the first call of kvm_reset_vcpu() for the guest, the new kvm flag is not set yet. So, KVM_ARM_VCPU_EL1_32BIT will be needed by the function (unless we pass the flag as an argument for the function or by any other way). > Also, we really should turn all these various bits in the kvm struct > into a set of flags. I have a patch posted there[1] for this, feel > free to pick it up. Thank you for the suggestion. But, kvm->arch.el1_reg_width is not a binary because it needs to indicate an uninitialized state. So, it won't fit perfectly with kvm->arch.flags, which is introduced by [1] as it is. Of course it's feasible by using 2 bits of the flags though... Thanks, Reiji > > Thanks, > > M. > > [1] https://lore.kernel.org/r/20211004174849.2831548-2-maz@kernel.org > > -- > Without deviation from the norm, progress is not possible.
On Thu, 10 Feb 2022 05:31:49 +0000, Reiji Watanabe <reijiw@google.com> wrote: > > Hi Marc, > > On Wed, Feb 9, 2022 at 4:04 AM Marc Zyngier <maz@kernel.org> wrote: > > > > Hi Reiji, > > > > On Wed, 09 Feb 2022 05:32:36 +0000, > > Reiji Watanabe <reijiw@google.com> wrote: > > > > > > Hi Marc, > > > > > > On Tue, Feb 8, 2022 at 6:41 AM Marc Zyngier <maz@kernel.org> wrote: > > > > > > > > In [1], I suggested another approach that didn't require extra state, > > > > and moved the existing checks under the kvm lock. What was wrong with > > > > that approach? > > > > > > With that approach, even for a vcpu that has a broken set of features, > > > which leads kvm_reset_vcpu() to fail for the vcpu, the vcpu->arch.features > > > are checked by other vCPUs' vcpu_allowed_register_width() until the > > > vcpu->arch.target is set to -1. > > > Due to this, I would think some or possibly all vCPUs' kvm_reset_vcpu() > > > may or may not fail (e.g. if userspace tries to configure vCPU#0 with > > > 32bit EL1, and vCPU#1 and #2 with 64 bit EL1, KVM_ARM_VCPU_INIT > > > for either vCPU#0, or both vCPU#1 and #2 should fail. But, with that > > > approach, it doesn't always work that way. Instead, KVM_ARM_VCPU_INIT > > > for all vCPUs could fail or KVM_ARM_VCPU_INIT for vCPU#0 and #1 could > > > fail while the one for CPU#2 works). > > > Also, even after the first KVM_RUN for vCPUs are already done, > > > (the first) KVM_ARM_VCPU_INIT for another vCPU could cause the > > > kvm_reset_vcpu() for those vCPUs to fail. > > > > > > I would think those behaviors are odd, and I wanted to avoid them. > > > > OK, fair enough. But then you need to remove most of the uses of > > KVM_ARM_VCPU_EL1_32BIT so that it is only used as a userspace > > interface and > > Yes, I will. > > > maybe not carried as part of the vcpu feature flag anymore. > > At the first call of kvm_reset_vcpu() for the guest, the new kvm > flag is not set yet. So, KVM_ARM_VCPU_EL1_32BIT will be needed > by the function (unless we pass the flag as an argument for the > function or by any other way). Which is why I said 'maybe'. It's not a big deal if the flags stays, but I don't want it evaluated further down the line. It is also pretty similar to HCR_EL2.RW, which we already test with vcpu_el1_is_32bit(). Overall, we need to reduce that state to be as simple as possible. > > > Also, we really should turn all these various bits in the kvm struct > > into a set of flags. I have a patch posted there[1] for this, feel > > free to pick it up. > > Thank you for the suggestion. But, kvm->arch.el1_reg_width is not > a binary because it needs to indicate an uninitialized state. So, it > won't fit perfectly with kvm->arch.flags, which is introduced by [1] > as it is. Of course it's feasible by using 2 bits of the flags though... 2 bits is what I had in mind (one bit to indicate that it has already been initialised, another to carry the actual width). Thanks, M.
Hi Marc, > > > Also, we really should turn all these various bits in the kvm struct > > > into a set of flags. I have a patch posted there[1] for this, feel > > > free to pick it up. > > > > Thank you for the suggestion. But, kvm->arch.el1_reg_width is not > > a binary because it needs to indicate an uninitialized state. So, it > > won't fit perfectly with kvm->arch.flags, which is introduced by [1] > > as it is. Of course it's feasible by using 2 bits of the flags though... > > 2 bits is what I had in mind (one bit to indicate that it has already > been initialised, another to carry the actual width). Understood. Then, I will take the patch and will work on v3. Thank you for all the comments! Regards, Reiji
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 2a5f7f38006f..c02b7caf2c82 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -102,6 +102,12 @@ struct kvm_s2_mmu { struct kvm_arch_memory_slot { }; +enum kvm_el1_reg_width { + EL1_WIDTH_UNINITIALIZED = 0, + EL1_32BIT, + EL1_64BIT, +}; + struct kvm_arch { struct kvm_s2_mmu mmu; @@ -137,6 +143,13 @@ struct kvm_arch { /* Memory Tagging Extension enabled for the guest */ bool mte_enabled; + + /* + * EL1 register width for the guest. + * This is set at the first KVM_ARM_VCPU_INIT for the guest based + * on whether the vcpu has KVM_ARM_VCPU_EL1_32BIT or not. + */ + enum kvm_el1_reg_width el1_reg_width; }; struct kvm_vcpu_fault_info { diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index e4727dc771bf..54ae8bf9d187 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -1058,6 +1058,32 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level, return -EINVAL; } +/* + * A guest can have either all 32bit or 64bit vcpus only. + * Either one the guest has is indicated in kvm->arch.el1_reg_width. + * Check if the vcpu's register width is consistent with + * kvm->arch.el1_reg_width. If kvm->arch.el1_reg_width is not set yet, + * set it based on the vcpu's KVM_ARM_VCPU_EL1_32BIT configuration. + */ +static int kvm_register_width_check_or_init(struct kvm_vcpu *vcpu) +{ + bool is32bit; + bool allowed = true; + struct kvm *kvm = vcpu->kvm; + + is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT); + + mutex_lock(&kvm->lock); + + if (kvm->arch.el1_reg_width == EL1_WIDTH_UNINITIALIZED) + kvm->arch.el1_reg_width = is32bit ? EL1_32BIT : EL1_64BIT; + else + allowed = (is32bit == (kvm->arch.el1_reg_width == EL1_32BIT)); + + mutex_unlock(&kvm->lock); + return allowed ? 0 : -EINVAL; +} + static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu, const struct kvm_vcpu_init *init) { @@ -1097,6 +1123,10 @@ static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu, /* Now we know what it is, we can reset it. */ ret = kvm_reset_vcpu(vcpu); + + if (!ret) + ret = kvm_register_width_check_or_init(vcpu); + if (ret) { vcpu->arch.target = -1; bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES); diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c index 426bd7fbc3fd..dbf2939a6a96 100644 --- a/arch/arm64/kvm/reset.c +++ b/arch/arm64/kvm/reset.c @@ -168,9 +168,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu) static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu) { - struct kvm_vcpu *tmp; bool is32bit; - int i; is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT); if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) && is32bit) @@ -180,12 +178,6 @@ static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu) if (kvm_has_mte(vcpu->kvm) && is32bit) return false; - /* Check that the vcpus are either all 32bit or all 64bit */ - kvm_for_each_vcpu(i, tmp, vcpu->kvm) { - if (vcpu_has_feature(tmp, KVM_ARM_VCPU_EL1_32BIT) != is32bit) - return false; - } - return true; }
KVM allows userspace to configure either all 32bit or 64bit vCPUs for a guest. At vCPU reset, vcpu_allowed_register_width() checks if the vcpu's register width is consistent with all other vCPUs'. Since the checking is done even against vCPUs that are not initialized (KVM_ARM_VCPU_INIT has not been done) yet, the uninitialized vCPUs are erroneously treated as 64bit vCPU, which causes the function to incorrectly detect a mixed-width VM. Introduce a new flag (el1_reg_width) in kvm_arch to indicates that the guest needs to be configured with all 32bit or 64bit vCPUs, and initialize it at the first KVM_ARM_VCPU_INIT for the guest. Check vcpu's register width against the flag at the vcpu's KVM_ARM_VCPU_INIT (instead of against other vCPUs' register width). Fixes: 66e94d5cafd4 ("KVM: arm64: Prevent mixed-width VM creation") Signed-off-by: Reiji Watanabe <reijiw@google.com> --- arch/arm64/include/asm/kvm_host.h | 13 +++++++++++++ arch/arm64/kvm/arm.c | 30 ++++++++++++++++++++++++++++++ arch/arm64/kvm/reset.c | 8 -------- 3 files changed, 43 insertions(+), 8 deletions(-) base-commit: 37144b2c855f9311c72f292125061d4a52d02856