Re: [PATCH v12 00/46] arm64: Support for Arm CCA in KVM

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

On Mon, Feb 16, 2026 at 02:27:02PM +0000, Steven Price wrote:
> On 16/02/2026 12:33, Steven Price wrote:
> > On 12/02/2026 17:48, Mathieu Poirier wrote:
> >> Hi Steven,
> >>
> >> On Wed, Dec 17, 2025 at 10:10:37AM +0000, Steven Price wrote:
> >>> This series adds support for running protected VMs using KVM under the
> >>> Arm Confidential Compute Architecture (CCA). I've changed the uAPI
> >>> following feedback from Marc.
> >>>
> >>> The main change is that rather than providing a multiplex CAP and
> >>> expecting the VMM to drive the different stages of realm construction,
> >>> there's now just a minimal interface and KVM performs the necessary
> >>> operations when needed.
> >>>
> >>> This series is lightly tested and is meant as a demonstration of the new
> >>> uAPI. There are a number of (known) rough corners in the implementation
> >>> that I haven't dealt with properly.
> >>>
> >>> In particular please note that this series is still targetting RMM v1.0.
> >>> There is an alpha quality version of RMM v2.0 available[1]. Feedback was
> >>> that there are a number of blockers for merging with RMM v1.0 and so I
> >>> expect to rework this series to support RMM v2.0 before it is merged.
> >>> That will necessarily involve reworking the implementation.
> >>>
> >>> Specifically I'm expecting improvements in:
> >>>
> >>>  * GIC handling - passing state in registers, and allowing the host to
> >>>    fully emulate the GIC by allowing trap bits to be set.
> >>>
> >>>  * PMU handling - again providing flexibility to the host's emulation.
> >>>
> >>>  * Page size/granule size mismatch. RMM v1.0 defines the granule as 4k,
> >>>    RMM v2.0 provide the option for the host to change the granule size.
> >>>    The intention is that Linux would simply set the granule size equal
> >>>    to its page size which will significantly simplify the management of
> >>>    granules.
> >>>
> >>>  * Some performance improvement from the use of range-based map/unmap
> >>>    RMI calls.
> >>>
> >>> This series is based on v6.19-rc1. It is also available as a git
> >>> repository:
> >>>
> >>> https://gitlab.arm.com/linux-arm/linux-cca cca-host/v12
> >>>
> >>> Work in progress changes for kvmtool are available from the git
> >>> repository below:
> >>>
> >>> https://gitlab.arm.com/linux-arm/kvmtool-cca cca/v10
> >>
> >> The first thing to note is that branch cca/v10 does not compile due to function
> >> realm_configure_parameters() not being called anywhere.  Marking the function as
> >> [[maybe_unused]] solved the problem on my side.
> > 
> > This is in the kvmtool code - and yes I agree "work in progress" is a
> > bit generous for the current state of that code, "horrid ugly hacks to
> > get things working" is probably more accurate ;)
> > 
> > The issue here is that the two things that realm_configure_parameters()
> > set up (hash algorithm and RPV) are currently unsupported with the Linux
> > changes, but will need to be reintroduced in the future. So the contents
> > of the functions which set this up (using the old uAPI) are just #if 0'd
> > out.
> > 
> > Depending on the compile flags the code will compile with a warning, but
> > using __attribute__((unused)) would at least make this clear. I'd want
> > to avoid the "[[maybe_unused]]" as it's not used elsewhere in the code
> > base and limits compatibility.
> > 
> >> Using the FVP emulator, booting a Realm that includes EDK2 in its boot stack
> >> worked.  If EDK2 is not part of the boot stack and a kernel is booted directly
> >> from lkvm, mounting the initrd fails.  Looking into this issue further, I see
> >> that from a Realm kernel's perspective, the content of the initrd is either
> >> encrypted or has been trampled on.  
> > 
> > I can reproduce that, a quick fix is to change INITRD_ALIGN:
> > 
> > #define INITRD_ALIGN	SZ_64K
> > 
> > But the code was meant to be able to deal with an unaligned initrd -
> > I'll see if I can figure out what's going wrong.
> 
> Looks like a simple bug in kvm_arm_realm_populate_ram() - it wasn't
> updating the source address when it had to align the start of the
> region. Simple fix below:
> 
> ---8<---
> diff --git a/arm/aarch64/realm.c b/arm/aarch64/realm.c
> --- a/arm/aarch64/realm.c
> +++ b/arm/aarch64/realm.c
> @@ -104,7 +104,7 @@ void kvm_arm_realm_populate_ram(struct kvm *kvm,
> unsigned long start,
> 
>         new_region->start = ALIGN_DOWN(start, SZ_64K);
>         new_region->file_end = ALIGN(start + size, SZ_64K);
> -       new_region->source = source;
> +       new_region->source = source - (start - new_region->start);

That also worked on my side.

> 
>         list_add_tail(&new_region->list, &realm_ram_regions);
>  }
> ---8<---
> 
> Thanks for the pointer, and I'll try to remember to include initrd
> testing in future.
> 

Very well.

Thanks for looking into this.

> Steve
>