Re: [RFC v1 01/25] linux-headers: Add RME related definitions

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Fri, Jul 10, 2026 at 11:09:43AM +1000, Gavin Shan wrote:
> On 7/8/26 8:42 AM, Mathieu Poirier wrote:
> > From: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > 
> > This is a temporary patch intended for testing purposes only. It provides
> > definitions related to supporting Realms by the QEMU-VMM.
> > 
> > Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> > ---
> >   linux-headers/asm-arm64/kvm.h |  9 +++++++++
> >   linux-headers/linux/kvm.h     | 21 +++++++++++++++++----
> >   2 files changed, 26 insertions(+), 4 deletions(-)
> > 
> > diff --git a/linux-headers/asm-arm64/kvm.h b/linux-headers/asm-arm64/kvm.h
> > index 6aefe7973814..4c08631ec7d2 100644
> > --- a/linux-headers/asm-arm64/kvm.h
> > +++ b/linux-headers/asm-arm64/kvm.h
> > @@ -208,6 +208,15 @@ struct kvm_arm_counter_offset {
> >   	__u64 reserved;
> >   };
> > +#define KVM_ARM_RMI_POPULATE_FLAGS_MEASURE     (1 << 0)
> > +struct kvm_arm_rmi_populate {
> > +	__u64 base;
> > +	__u64 size;
> > +	__u64 source_uaddr;
> > +	__u32 flags;
> > +	__u32 reserved;
> > +};
> > +
> >   #define KVM_ARM_TAGS_TO_GUEST		0
> >   #define KVM_ARM_TAGS_FROM_GUEST		1
> > diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
> > index 50e87ed72c20..dae6e5ba8457 100644
> > --- a/linux-headers/linux/kvm.h
> > +++ b/linux-headers/linux/kvm.h
> > @@ -685,11 +685,21 @@ struct kvm_enable_cap {
> >   #define KVM_S390_SIE_PAGE_OFFSET 1
> >   /*
> > - * On arm64, machine type can be used to request the physical
> > - * address size for the VM. Bits[7-0] are reserved for the guest
> > - * PA size shift (i.e, log2(PA_Size)). For backward compatibility,
> > - * value 0 implies the default IPA size, 40bits.
> > + * On arm64, machine type can be used to request both the machine type and
> > + * the physical address size for the VM.
> > + *
> > + * Bits[31-30] are reserved for the ARM specific machine type.
> > + *
> > + * Bits[7-0] are reserved for the guest PA size shift (i.e, log2(PA_Size)).
> > + * For backward compatibility, value 0 implies the default IPA size, 40bits.
> >    */
> > +#define KVM_VM_TYPE_ARM_SHIFT		30
> > +#define KVM_VM_TYPE_ARM_MASK		(0x3ULL << KVM_VM_TYPE_ARM_SHIFT)
> > +#define KVM_VM_TYPE_ARM(_type)		\
> > +	(((_type) << KVM_VM_TYPE_ARM_SHIFT) & KVM_VM_TYPE_ARM_MASK)
> > +#define KVM_VM_TYPE_ARM_NORMAL		KVM_VM_TYPE_ARM(0)
> > +#define KVM_VM_TYPE_ARM_REALM		KVM_VM_TYPE_ARM(1)
> > +
> >   #define KVM_VM_TYPE_ARM_IPA_SIZE_MASK	0xffULL
> >   #define KVM_VM_TYPE_ARM_IPA_SIZE(x)		\
> >   	((x) & KVM_VM_TYPE_ARM_IPA_SIZE_MASK)
> 
> The definitions in this section aren't exactly same to that in (v14) host series,
> leading to KVM_VM_TYPE_ARM_REALM = 0 in my environment and the realm guest can't
> be started with the following error message. At least, KVM_VM_TYPE_ARM_MASK has
> been redefined with different values.
> 
>   qemu-system-aarch64: KVM does not support guest_memfd

I agree with you.  Although outdated the above should work - left shifting
0x3ULL by 30 seems to be causing issues.  

> 
>   ----> linux-headers/linux/kvm.h
> 
>   #define KVM_VM_TYPE_ARM_SHIFT          30
>   #define KVM_VM_TYPE_ARM_MASK           (0x3ULL << KVM_VM_TYPE_ARM_SHIFT)
> 
>   #define KVM_VM_TYPE_ARM_MASK           (KVM_VM_TYPE_ARM_IPA_SIZE_MASK | \
>                                           KVM_VM_TYPE_ARM_PROTECTED)
> 
> After syncing the definitions with those in (v14) host series, I'm able to boot
> a simple realm guest (no virtio devices) with one warning.
> 
>   qemu-system-aarch64: Failed to enable KVM_CAP_ARM_NISV_TO_USER cap

Right, that one is useless.

Both issues reported here will be addressed in the next revision.

> 
> Thanks,
> Gavin
> 
> > @@ -719,6 +729,8 @@ struct kvm_enable_cap {
> >   #define KVM_GET_EMULATED_CPUID	  _IOWR(KVMIO, 0x09, struct kvm_cpuid2)
> >   #define KVM_GET_MSR_FEATURE_INDEX_LIST    _IOWR(KVMIO, 0x0a, struct kvm_msr_list)
> > +#define KVM_ARM_RMI_POPULATE	  _IOWR(KVMIO, 0xd7, struct kvm_arm_rmi_populate)
> > +
> >   /*
> >    * Extension capability list.
> >    */
> > @@ -985,6 +997,7 @@ struct kvm_enable_cap {
> >   #define KVM_CAP_S390_USER_OPEREXEC 246
> >   #define KVM_CAP_S390_KEYOP 247
> >   #define KVM_CAP_S390_VSIE_ESAMODE 248
> > +#define KVM_CAP_ARM_RMI 249
> >   struct kvm_irq_routing_irqchip {
> >   	__u32 irqchip;
>