| Message ID | 1530270944-11351-16-git-send-email-suzuki.poulose@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 29/06/18 12:15, Suzuki K Poulose wrote: > Allow specifying the physical address size for a new VM via > the kvm_type argument for KVM_CREATE_VM ioctl. This allows > us to finalise the stage2 page table format as early as possible > and hence perform the right checks on the memory slots without > complication. The size is encoded as Log2(PA_Size) in the bits[7:0] > of the type field and can encode more information in the future if > required. The IPA size is still capped at 40bits. Can't we relax this? There is no technical reason (AFAICS) not to allow going down to 36bit IPA if the user has requested it. If we run on a 36bit IPA system, the default would fail. But if the user specified "please give me a 36bit IPA VM", we could satisfy that requirement and allow them to run their stupidly small guest! Thanks, M.
On 02/07/18 14:13, Marc Zyngier wrote: > On 29/06/18 12:15, Suzuki K Poulose wrote: >> Allow specifying the physical address size for a new VM via >> the kvm_type argument for KVM_CREATE_VM ioctl. This allows >> us to finalise the stage2 page table format as early as possible >> and hence perform the right checks on the memory slots without >> complication. The size is encoded as Log2(PA_Size) in the bits[7:0] >> of the type field and can encode more information in the future if >> required. The IPA size is still capped at 40bits. > > Can't we relax this? There is no technical reason (AFAICS) not to allow > going down to 36bit IPA if the user has requested it. Sure, we can. > > If we run on a 36bit IPA system, the default would fail. But if the user > specified "please give me a 36bit IPA VM", we could satisfy that > requirement and allow them to run their stupidly small guest! Absolutely. I will fix this in the next version. Cheers Suzuki
Hi Suzuki, On Fri, Jun 29, 2018 at 12:15:35PM +0100, Suzuki K Poulose wrote: > Allow specifying the physical address size for a new VM via > the kvm_type argument for KVM_CREATE_VM ioctl. This allows > us to finalise the stage2 page table format as early as possible > and hence perform the right checks on the memory slots without > complication. The size is encoded as Log2(PA_Size) in the bits[7:0] > of the type field and can encode more information in the future if > required. The IPA size is still capped at 40bits. > > Cc: Marc Zyngier <marc.zyngier@arm.com> > Cc: Christoffer Dall <cdall@kernel.org> > Cc: Peter Maydel <peter.maydell@linaro.org> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > --- > arch/arm/include/asm/kvm_mmu.h | 2 ++ > arch/arm64/include/asm/kvm_arm.h | 10 +++------- > arch/arm64/include/asm/kvm_mmu.h | 2 ++ > include/uapi/linux/kvm.h | 10 ++++++++++ > virt/kvm/arm/arm.c | 24 ++++++++++++++++++++++-- > 5 files changed, 39 insertions(+), 9 deletions(-) [...] > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 4df9bb6..fa4cab0 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -751,6 +751,16 @@ struct kvm_ppc_resize_hpt { > #define KVM_S390_SIE_PAGE_OFFSET 1 > > /* > + * On arm/arm64, machine type can be used to request the physical > + * address size for the VM. Bits [7-0] have been reserved for the > + * PA size shift (i.e, log2(PA_Size)). For backward compatibility, > + * value 0 implies the default IPA size, which is 40bits. > + */ > +#define KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK 0xff > +#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x) \ > + ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK) This seems like you're allocating quite a lot of bits in a non-extensible interface to a fairly esoteric parameter. Would it be better to add another ioctl, or condense the number of sizes you support instead? Will
On 07/04/2018 04:51 PM, Will Deacon wrote: > Hi Suzuki, > > On Fri, Jun 29, 2018 at 12:15:35PM +0100, Suzuki K Poulose wrote: >> Allow specifying the physical address size for a new VM via >> the kvm_type argument for KVM_CREATE_VM ioctl. This allows >> us to finalise the stage2 page table format as early as possible >> and hence perform the right checks on the memory slots without >> complication. The size is encoded as Log2(PA_Size) in the bits[7:0] >> of the type field and can encode more information in the future if >> required. The IPA size is still capped at 40bits. >> >> Cc: Marc Zyngier <marc.zyngier@arm.com> >> Cc: Christoffer Dall <cdall@kernel.org> >> Cc: Peter Maydel <peter.maydell@linaro.org> >> Cc: Paolo Bonzini <pbonzini@redhat.com> >> Cc: Radim Krčmář <rkrcmar@redhat.com> >> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >> --- >> arch/arm/include/asm/kvm_mmu.h | 2 ++ >> arch/arm64/include/asm/kvm_arm.h | 10 +++------- >> arch/arm64/include/asm/kvm_mmu.h | 2 ++ >> include/uapi/linux/kvm.h | 10 ++++++++++ >> virt/kvm/arm/arm.c | 24 ++++++++++++++++++++++-- >> 5 files changed, 39 insertions(+), 9 deletions(-) > > [...] > >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >> index 4df9bb6..fa4cab0 100644 >> --- a/include/uapi/linux/kvm.h >> +++ b/include/uapi/linux/kvm.h >> @@ -751,6 +751,16 @@ struct kvm_ppc_resize_hpt { >> #define KVM_S390_SIE_PAGE_OFFSET 1 >> >> /* >> + * On arm/arm64, machine type can be used to request the physical >> + * address size for the VM. Bits [7-0] have been reserved for the >> + * PA size shift (i.e, log2(PA_Size)). For backward compatibility, >> + * value 0 implies the default IPA size, which is 40bits. >> + */ >> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK 0xff >> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x) \ >> + ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK) > > This seems like you're allocating quite a lot of bits in a non-extensible > interface to a fairly esoteric parameter. Would it be better to add another > ioctl, or condense the number of sizes you support instead? As I explained in the other thread, we need the size as soon as the VM is created. The major challenge is keeping the backward compatibility by mapping 0 to 40bits. I will give it a thought. Suzuki
On 04/07/18 23:03, Suzuki K Poulose wrote: > On 07/04/2018 04:51 PM, Will Deacon wrote: >> Hi Suzuki, >> >> On Fri, Jun 29, 2018 at 12:15:35PM +0100, Suzuki K Poulose wrote: >>> Allow specifying the physical address size for a new VM via >>> the kvm_type argument for KVM_CREATE_VM ioctl. This allows >>> us to finalise the stage2 page table format as early as possible >>> and hence perform the right checks on the memory slots without >>> complication. The size is encoded as Log2(PA_Size) in the bits[7:0] >>> of the type field and can encode more information in the future if >>> required. The IPA size is still capped at 40bits. >>> >>> Cc: Marc Zyngier <marc.zyngier@arm.com> >>> Cc: Christoffer Dall <cdall@kernel.org> >>> Cc: Peter Maydel <peter.maydell@linaro.org> >>> Cc: Paolo Bonzini <pbonzini@redhat.com> >>> Cc: Radim Krčmář <rkrcmar@redhat.com> >>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >>> --- >>> arch/arm/include/asm/kvm_mmu.h | 2 ++ >>> arch/arm64/include/asm/kvm_arm.h | 10 +++------- >>> arch/arm64/include/asm/kvm_mmu.h | 2 ++ >>> include/uapi/linux/kvm.h | 10 ++++++++++ >>> virt/kvm/arm/arm.c | 24 ++++++++++++++++++++++-- >>> 5 files changed, 39 insertions(+), 9 deletions(-) >> >> [...] >> >>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >>> index 4df9bb6..fa4cab0 100644 >>> --- a/include/uapi/linux/kvm.h >>> +++ b/include/uapi/linux/kvm.h >>> @@ -751,6 +751,16 @@ struct kvm_ppc_resize_hpt { >>> #define KVM_S390_SIE_PAGE_OFFSET 1 >>> /* >>> + * On arm/arm64, machine type can be used to request the physical >>> + * address size for the VM. Bits [7-0] have been reserved for the >>> + * PA size shift (i.e, log2(PA_Size)). For backward compatibility, >>> + * value 0 implies the default IPA size, which is 40bits. >>> + */ >>> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK 0xff >>> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x) \ >>> + ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK) >> >> This seems like you're allocating quite a lot of bits in a non-extensible >> interface to a fairly esoteric parameter. Would it be better to add another >> ioctl, or condense the number of sizes you support instead? > > As I explained in the other thread, we need the size as soon as the VM > is created. The major challenge is keeping the backward compatibility by > mapping 0 to 40bits. I will give it a thought. Here is one option. We could re-use the {V}TCR_ELx.{I}PS field format, which occupies 3 bits and has the following definitions. (ID_AA64MMFR0_EL1:PARange also has the field definitions, except that the field is 4bits wide, but only 3bits are used) 000 32 bits, 4GB. 001 36 bits, 64GB. 010 40 bits, 1TB. 011 42 bits, 4TB. 100 44 bits, 16TB. 101 48 bits, 256TB. 110 52 bits, 4PB But we need to map 0 => 40bits IPA to make our ABI backward compatible. So we could use the additional one bit to indicate that IPA size is requested in the 3 bits. i.e, machine_type: Bit [2:0] - Requested IPA size. Values follow VTCR_EL2.PS format. Bit [3] - 1 => IPA Size bits (Bits[2:0]) requested. 0 => Not requested The only minor down side is restricting to the predefined values above, which is not a real issue for a VM. Thoughts ? Suzuki
On 06/07/18 14:49, Suzuki K Poulose wrote: > On 04/07/18 23:03, Suzuki K Poulose wrote: >> On 07/04/2018 04:51 PM, Will Deacon wrote: >>> Hi Suzuki, >>> >>> On Fri, Jun 29, 2018 at 12:15:35PM +0100, Suzuki K Poulose wrote: >>>> Allow specifying the physical address size for a new VM via >>>> the kvm_type argument for KVM_CREATE_VM ioctl. This allows >>>> us to finalise the stage2 page table format as early as possible >>>> and hence perform the right checks on the memory slots without >>>> complication. The size is encoded as Log2(PA_Size) in the bits[7:0] >>>> of the type field and can encode more information in the future if >>>> required. The IPA size is still capped at 40bits. >>>> >>>> Cc: Marc Zyngier <marc.zyngier@arm.com> >>>> Cc: Christoffer Dall <cdall@kernel.org> >>>> Cc: Peter Maydel <peter.maydell@linaro.org> >>>> Cc: Paolo Bonzini <pbonzini@redhat.com> >>>> Cc: Radim Krčmář <rkrcmar@redhat.com> >>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >>>> --- >>>> arch/arm/include/asm/kvm_mmu.h | 2 ++ >>>> arch/arm64/include/asm/kvm_arm.h | 10 +++------- >>>> arch/arm64/include/asm/kvm_mmu.h | 2 ++ >>>> include/uapi/linux/kvm.h | 10 ++++++++++ >>>> virt/kvm/arm/arm.c | 24 ++++++++++++++++++++++-- >>>> 5 files changed, 39 insertions(+), 9 deletions(-) >>> >>> [...] >>> >>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >>>> index 4df9bb6..fa4cab0 100644 >>>> --- a/include/uapi/linux/kvm.h >>>> +++ b/include/uapi/linux/kvm.h >>>> @@ -751,6 +751,16 @@ struct kvm_ppc_resize_hpt { >>>> #define KVM_S390_SIE_PAGE_OFFSET 1 >>>> /* >>>> + * On arm/arm64, machine type can be used to request the physical >>>> + * address size for the VM. Bits [7-0] have been reserved for the >>>> + * PA size shift (i.e, log2(PA_Size)). For backward compatibility, >>>> + * value 0 implies the default IPA size, which is 40bits. >>>> + */ >>>> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK 0xff >>>> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x) \ >>>> + ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK) >>> >>> This seems like you're allocating quite a lot of bits in a non-extensible >>> interface to a fairly esoteric parameter. Would it be better to add another >>> ioctl, or condense the number of sizes you support instead? >> >> As I explained in the other thread, we need the size as soon as the VM >> is created. The major challenge is keeping the backward compatibility by >> mapping 0 to 40bits. I will give it a thought. > > Here is one option. We could re-use the {V}TCR_ELx.{I}PS field format, which > occupies 3 bits and has the following definitions. (ID_AA64MMFR0_EL1:PARange > also has the field definitions, except that the field is 4bits wide, but > only 3bits are used) > > 000 32 bits, 4GB. > 001 36 bits, 64GB. > 010 40 bits, 1TB. > 011 42 bits, 4TB. > 100 44 bits, 16TB. > 101 48 bits, 256TB. > 110 52 bits, 4PB > > But we need to map 0 => 40bits IPA to make our ABI backward compatible. So > we could use the additional one bit to indicate that IPA size is requested > in the 3 bits. > > i.e, > > machine_type: > > Bit [2:0] - Requested IPA size. Values follow VTCR_EL2.PS format. > > Bit [3] - 1 => IPA Size bits (Bits[2:0]) requested. > 0 => Not requested > > The only minor down side is restricting to the predefined values above, > which is not a real issue for a VM. > > Thoughts ? I'd be very wary of using that 4th bit to do something that is not in the architecture. We have only a single value left to be used (0b111), and then your scheme clashes with the architecture definition. I'd rather encode things in a way that is independent from the architecture, and be done with it. You can map 0 to 40bits, and we have the ability to express all values the architecture has (just in a different order). Thanks, M.
On 07/06/2018 04:09 PM, Marc Zyngier wrote: > On 06/07/18 14:49, Suzuki K Poulose wrote: >> On 04/07/18 23:03, Suzuki K Poulose wrote: >>> On 07/04/2018 04:51 PM, Will Deacon wrote: >>>> Hi Suzuki, >>>> >>>> On Fri, Jun 29, 2018 at 12:15:35PM +0100, Suzuki K Poulose wrote: >>>>> Allow specifying the physical address size for a new VM via >>>>> the kvm_type argument for KVM_CREATE_VM ioctl. This allows >>>>> us to finalise the stage2 page table format as early as possible >>>>> and hence perform the right checks on the memory slots without >>>>> complication. The size is encoded as Log2(PA_Size) in the bits[7:0] >>>>> of the type field and can encode more information in the future if >>>>> required. The IPA size is still capped at 40bits. >>>>> >>>>> Cc: Marc Zyngier <marc.zyngier@arm.com> >>>>> Cc: Christoffer Dall <cdall@kernel.org> >>>>> Cc: Peter Maydel <peter.maydell@linaro.org> >>>>> Cc: Paolo Bonzini <pbonzini@redhat.com> >>>>> Cc: Radim Krčmář <rkrcmar@redhat.com> >>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >>>>> --- >>>>> arch/arm/include/asm/kvm_mmu.h | 2 ++ >>>>> arch/arm64/include/asm/kvm_arm.h | 10 +++------- >>>>> arch/arm64/include/asm/kvm_mmu.h | 2 ++ >>>>> include/uapi/linux/kvm.h | 10 ++++++++++ >>>>> virt/kvm/arm/arm.c | 24 ++++++++++++++++++++++-- >>>>> 5 files changed, 39 insertions(+), 9 deletions(-) >>>> >>>> [...] >>>> >>>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >>>>> index 4df9bb6..fa4cab0 100644 >>>>> --- a/include/uapi/linux/kvm.h >>>>> +++ b/include/uapi/linux/kvm.h >>>>> @@ -751,6 +751,16 @@ struct kvm_ppc_resize_hpt { >>>>> #define KVM_S390_SIE_PAGE_OFFSET 1 >>>>> /* >>>>> + * On arm/arm64, machine type can be used to request the physical >>>>> + * address size for the VM. Bits [7-0] have been reserved for the >>>>> + * PA size shift (i.e, log2(PA_Size)). For backward compatibility, >>>>> + * value 0 implies the default IPA size, which is 40bits. >>>>> + */ >>>>> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK 0xff >>>>> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x) \ >>>>> + ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK) >>>> >>>> This seems like you're allocating quite a lot of bits in a non-extensible >>>> interface to a fairly esoteric parameter. Would it be better to add another >>>> ioctl, or condense the number of sizes you support instead? >>> >>> As I explained in the other thread, we need the size as soon as the VM >>> is created. The major challenge is keeping the backward compatibility by >>> mapping 0 to 40bits. I will give it a thought. >> >> Here is one option. We could re-use the {V}TCR_ELx.{I}PS field format, which >> occupies 3 bits and has the following definitions. (ID_AA64MMFR0_EL1:PARange >> also has the field definitions, except that the field is 4bits wide, but >> only 3bits are used) >> >> 000 32 bits, 4GB. >> 001 36 bits, 64GB. >> 010 40 bits, 1TB. >> 011 42 bits, 4TB. >> 100 44 bits, 16TB. >> 101 48 bits, 256TB. >> 110 52 bits, 4PB >> >> But we need to map 0 => 40bits IPA to make our ABI backward compatible. So >> we could use the additional one bit to indicate that IPA size is requested >> in the 3 bits. >> >> i.e, >> >> machine_type: >> >> Bit [2:0] - Requested IPA size. Values follow VTCR_EL2.PS format. >> >> Bit [3] - 1 => IPA Size bits (Bits[2:0]) requested. >> 0 => Not requested >> >> The only minor down side is restricting to the predefined values above, >> which is not a real issue for a VM. >> >> Thoughts ? > > I'd be very wary of using that 4th bit to do something that is not in > the architecture. We have only a single value left to be used (0b111), > and then your scheme clashes with the architecture definition. I agree. However, if we ever go beyond the 3bits in PARange, we have an issue with {V}TCR counter part. But lets not take that chance. > > I'd rather encode things in a way that is independent from the > architecture, and be done with it. You can map 0 to 40bits, and we have > the ability to express all values the architecture has (just in a > different order). The other option I can think of is encoding a signed number which is the difference of the IPA from 40. But that would need 5 bits if we were to encode it as it is. And if we want to squeeze it in 4bit, we could store half the difference (limiting the IPA limit to even numbers). i.e IPA = 40 + 2 * sign_extend(bits[3:0); Suzuki
On Fri, Jul 06, 2018 at 05:39:00PM +0100, Suzuki K Poulose wrote: > On 07/06/2018 04:09 PM, Marc Zyngier wrote: > >On 06/07/18 14:49, Suzuki K Poulose wrote: > >>On 04/07/18 23:03, Suzuki K Poulose wrote: > >>>On 07/04/2018 04:51 PM, Will Deacon wrote: > >>>>Hi Suzuki, > >>>> > >>>>On Fri, Jun 29, 2018 at 12:15:35PM +0100, Suzuki K Poulose wrote: > >>>>>Allow specifying the physical address size for a new VM via > >>>>>the kvm_type argument for KVM_CREATE_VM ioctl. This allows > >>>>>us to finalise the stage2 page table format as early as possible > >>>>>and hence perform the right checks on the memory slots without > >>>>>complication. The size is encoded as Log2(PA_Size) in the bits[7:0] > >>>>>of the type field and can encode more information in the future if > >>>>>required. The IPA size is still capped at 40bits. > >>>>> > >>>>>Cc: Marc Zyngier <marc.zyngier@arm.com> > >>>>>Cc: Christoffer Dall <cdall@kernel.org> > >>>>>Cc: Peter Maydel <peter.maydell@linaro.org> > >>>>>Cc: Paolo Bonzini <pbonzini@redhat.com> > >>>>>Cc: Radim Krčmář <rkrcmar@redhat.com> > >>>>>Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > >>>>>--- > >>>>> arch/arm/include/asm/kvm_mmu.h | 2 ++ > >>>>> arch/arm64/include/asm/kvm_arm.h | 10 +++------- > >>>>> arch/arm64/include/asm/kvm_mmu.h | 2 ++ > >>>>> include/uapi/linux/kvm.h | 10 ++++++++++ > >>>>> virt/kvm/arm/arm.c | 24 ++++++++++++++++++++++-- > >>>>> 5 files changed, 39 insertions(+), 9 deletions(-) > >>>> > >>>>[...] > >>>> > >>>>>diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > >>>>>index 4df9bb6..fa4cab0 100644 > >>>>>--- a/include/uapi/linux/kvm.h > >>>>>+++ b/include/uapi/linux/kvm.h > >>>>>@@ -751,6 +751,16 @@ struct kvm_ppc_resize_hpt { > >>>>> #define KVM_S390_SIE_PAGE_OFFSET 1 > >>>>> /* > >>>>>+ * On arm/arm64, machine type can be used to request the physical > >>>>>+ * address size for the VM. Bits [7-0] have been reserved for the > >>>>>+ * PA size shift (i.e, log2(PA_Size)). For backward compatibility, > >>>>>+ * value 0 implies the default IPA size, which is 40bits. > >>>>>+ */ > >>>>>+#define KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK 0xff > >>>>>+#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x) \ > >>>>>+ ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK) > >>>> > >>>>This seems like you're allocating quite a lot of bits in a non-extensible > >>>>interface to a fairly esoteric parameter. Would it be better to add another > >>>>ioctl, or condense the number of sizes you support instead? > >>> > >>>As I explained in the other thread, we need the size as soon as the VM > >>>is created. The major challenge is keeping the backward compatibility by > >>>mapping 0 to 40bits. I will give it a thought. > >> > >>Here is one option. We could re-use the {V}TCR_ELx.{I}PS field format, which > >>occupies 3 bits and has the following definitions. (ID_AA64MMFR0_EL1:PARange > >>also has the field definitions, except that the field is 4bits wide, but > >>only 3bits are used) > >> > >>000 32 bits, 4GB. > >>001 36 bits, 64GB. > >>010 40 bits, 1TB. > >>011 42 bits, 4TB. > >>100 44 bits, 16TB. > >>101 48 bits, 256TB. > >>110 52 bits, 4PB > >> > >>But we need to map 0 => 40bits IPA to make our ABI backward compatible. So > >>we could use the additional one bit to indicate that IPA size is requested > >>in the 3 bits. > >> > >>i.e, > >> > >>machine_type: > >> > >>Bit [2:0] - Requested IPA size. Values follow VTCR_EL2.PS format. > >> > >>Bit [3] - 1 => IPA Size bits (Bits[2:0]) requested. > >> 0 => Not requested > >> > >>The only minor down side is restricting to the predefined values above, > >>which is not a real issue for a VM. > >> > >>Thoughts ? > > > >I'd be very wary of using that 4th bit to do something that is not in > >the architecture. We have only a single value left to be used (0b111), > >and then your scheme clashes with the architecture definition. > > I agree. However, if we ever go beyond the 3bits in PARange, we have an > issue with {V}TCR counter part. But lets not take that chance. > > > > >I'd rather encode things in a way that is independent from the > >architecture, and be done with it. You can map 0 to 40bits, and we have > >the ability to express all values the architecture has (just in a > >different order). > > The other option I can think of is encoding a signed number which is the > difference of the IPA from 40. But that would need 5 bits if we were to > encode it as it is. And if we want to squeeze it in 4bit, we could store > half the difference (limiting the IPA limit to even numbers). > > i.e IPA = 40 + 2 * sign_extend(bits[3:0); I came across similar issues when trying to work out how to enable SVE for KVM. In the end I reduced this to a per-vcpu feature, but it means that there is no global opt-in for the SVE-specific KVM API extensions: That's a bit gross, because SVE may require a change to the way vcpus are initialised. The set of supported SVE vector lengths needs to be set somehow before the vcpu is set running, but it's tricky do do that without a new ioctl -- which would mean that if SVE is enabled for a vcpu then the vcpu is not considered runnable until the new magic ioctl is called. Opting into that semantic change globally at VM creation time might be preferable. On the SVE side, this is still very much subject to review/change. Here: The KVM_CREATE_VM init argument seems undefined by the KVM core code and is available for arches to abuse in creative ways. x86 and arm have nothing here and reject non-zero values with -EINVAL; s390 treats it as a bitmask, and defines a sincle feature-like bit here; powerpc treats it as an enumeration of VM types. If we want to be extensible, we could a) Pass a pointer in type, and come up with some extensible VM parameter struct for it to point to (which then wouldn't need a cryptic compressed encoding), or b) Introduce a new "KVM_CREATE_VM2" variant that either takes such an argument, or mandates a parameter negotiation phase involving additional ioctls before marking the VM as ready for vcpu and device creation. (a) feels like an easy backwards-compatible approach, but cannot be readily adopted by other arches (maybe not an issue). (b) might be considered overengineered, so it would need a bit of thought. Wedging arguments into a few bits in the type argument feels awkward, and may be regretted later if we run out of bits, or something can't be represented in the chosen encoding. Cheers ---Dave
diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h index d86f8dd..bcc3dd9 100644 --- a/arch/arm/include/asm/kvm_mmu.h +++ b/arch/arm/include/asm/kvm_mmu.h @@ -385,6 +385,8 @@ static inline u32 kvm_get_ipa_limit(void) return KVM_PHYS_SHIFT; } +static inline void kvm_config_stage2(struct kvm *kvm, u32 ipa_shift) {} + #endif /* !__ASSEMBLY__ */ #endif /* __ARM_KVM_MMU_H__ */ diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h index b02c316..2e90942 100644 --- a/arch/arm64/include/asm/kvm_arm.h +++ b/arch/arm64/include/asm/kvm_arm.h @@ -128,19 +128,15 @@ #define VTCR_EL2_T0SZ(x) TCR_T0SZ(x) /* - * We configure the Stage-2 page tables to always restrict the IPA space to be - * 40 bits wide (T0SZ = 24). Systems with a PARange smaller than 40 bits are - * not known to exist and will break with this configuration. + * We configure the Stage-2 page tables based on the requested size of + * IPA for each VM. The default size is set to 40bits and is not allowed + * go below that limit (for backward compatibility). * * VTCR_EL2.PS is extracted from ID_AA64MMFR0_EL1.PARange at boot time * (see hyp-init.S). * * VTCR_EL2.SL0 and T0SZ are configured per VM at runtime before switching to * the VM. - * - * Note that when using 4K pages, we concatenate two first level page tables - * together. With 16K pages, we concatenate 16 first level page tables. - * */ #define VTCR_EL2_COMMON_BITS (VTCR_EL2_SH0_INNER | VTCR_EL2_ORGN0_WBWA | \ diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h index b4564d8..f3fb05a3 100644 --- a/arch/arm64/include/asm/kvm_mmu.h +++ b/arch/arm64/include/asm/kvm_mmu.h @@ -537,5 +537,7 @@ static inline u32 kvm_get_ipa_limit(void) return KVM_PHYS_SHIFT; } +static inline void kvm_config_stage2(struct kvm *kvm, u32 ipa_shift) {} + #endif /* __ASSEMBLY__ */ #endif /* __ARM64_KVM_MMU_H__ */ diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 4df9bb6..fa4cab0 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -751,6 +751,16 @@ struct kvm_ppc_resize_hpt { #define KVM_S390_SIE_PAGE_OFFSET 1 /* + * On arm/arm64, machine type can be used to request the physical + * address size for the VM. Bits [7-0] have been reserved for the + * PA size shift (i.e, log2(PA_Size)). For backward compatibility, + * value 0 implies the default IPA size, which is 40bits. + */ +#define KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK 0xff +#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x) \ + ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK) + +/* * ioctls for /dev/kvm fds: */ #define KVM_GET_API_VERSION _IO(KVMIO, 0x00) diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index 0d99e67..1085761 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -112,6 +112,25 @@ void kvm_arch_check_processor_compat(void *rtn) } +static int kvm_arch_config_vm(struct kvm *kvm, unsigned long type) +{ + u32 ipa_shift = KVM_VM_TYPE_ARM_PHYS_SHIFT(type); + + /* + * Make sure the size, if specified, is within the range of + * default size and supported maximum limit. + */ + if (ipa_shift) { + if (ipa_shift < KVM_PHYS_SHIFT || ipa_shift > kvm_ipa_limit) + return -EINVAL; + } else { + ipa_shift = KVM_PHYS_SHIFT; + } + + kvm_config_stage2(kvm, ipa_shift); + return 0; +} + /** * kvm_arch_init_vm - initializes a VM data structure * @kvm: pointer to the KVM struct @@ -120,8 +139,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) { int ret, cpu; - if (type) - return -EINVAL; + ret = kvm_arch_config_vm(kvm, type); + if (ret) + return ret; kvm->arch.last_vcpu_ran = alloc_percpu(typeof(*kvm->arch.last_vcpu_ran)); if (!kvm->arch.last_vcpu_ran)
Allow specifying the physical address size for a new VM via the kvm_type argument for KVM_CREATE_VM ioctl. This allows us to finalise the stage2 page table format as early as possible and hence perform the right checks on the memory slots without complication. The size is encoded as Log2(PA_Size) in the bits[7:0] of the type field and can encode more information in the future if required. The IPA size is still capped at 40bits. Cc: Marc Zyngier <marc.zyngier@arm.com> Cc: Christoffer Dall <cdall@kernel.org> Cc: Peter Maydel <peter.maydell@linaro.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> --- arch/arm/include/asm/kvm_mmu.h | 2 ++ arch/arm64/include/asm/kvm_arm.h | 10 +++------- arch/arm64/include/asm/kvm_mmu.h | 2 ++ include/uapi/linux/kvm.h | 10 ++++++++++ virt/kvm/arm/arm.c | 24 ++++++++++++++++++++++-- 5 files changed, 39 insertions(+), 9 deletions(-)