Re: [PATCH v1 00/17] [RISC-V] virtual interrupt controller (vAPLIC/vIMSIC) support

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.07.2026 18:01, Oleksii Kurochko wrote:
> Hi all,
> 
> This series adds the initial virtual interrupt controller (vINTC) support
> for RISC-V guests in Xen, based on the Advanced Interrupt Architecture
> (AIA): a virtual APLIC (vAPLIC) in MSI mode backed by a virtual IMSIC
> (vIMSIC) using hardware guest interrupt files.
> 
> Rather than emulating APLIC in direct-delivery mode (which requires
> trap-and-emulate for every interrupt and is costly), the series targets
> IMSIC from the start. AIA lets a hart implement several "guest interrupt
> files" (up to GEILEN), so external interrupts can be delivered to a vCPU
> directly by hardware via the VGEIN field of hstatus, without a hypervisor
> round-trip. Xen only has to emulate the APLIC MMIO programming interface
> and route the guest's intent onto the physical MSI topology; interrupt
> delivery itself stays in hardware.
> 
> The work breaks down into a few logical blocks:
> 
> Physical APLIC/AIA groundwork (patches 1-3)
>   - Correctly track IRQ_DISABLED across runtime enable/disable and order
>     the ->status update against the IMSIC CSR write.
>   - Per-pCPU VGEIN (guest interrupt file) allocator: assign/release a
>     hardware guest file to a vCPU and program hstatus.VGEIN.
>   - Add the missing APLIC register offsets/masks needed by both the
>     physical and virtual APLIC code (no functional change).
> 
> Device-agnostic MMIO dispatch + vAPLIC emulation (patches 4-5)
>   - A per-domain MMIO handler table modelled on Arm's framework, so
>     emulated devices self-register their GPA ranges and the fault path
>     stays agnostic via a single try_handle_mmio() entry point.
>   - vAPLIC MMIO read/write emulation. Writes are gated by the domain's
>     authorised-IRQ bitmap so a guest cannot touch interrupts it does not
>     own, and TARGET writes are translated from virtual to physical
>     hart/guest-file indices. Delegation (SOURCECFG.D) is not yet
>     supported.
> 
> vIMSIC guest interrupt files and state (patches 6-9)
>   - Stage-2 map a vCPU's physical guest interrupt file to the fixed
>     per-vCPU GPA page the guest expects at offset 0.
>   - vcpu_aia_init(): assign a VGEIN, map its guest file and record the
>     IMSIC state as a consistent unit.
>   - IMSIC state save/restore (currently tracking which pCPU owns the
>     guest file, needed because the pCPU id is part of the MSI address).
>   - has_msi_support() helper to decide whether IMSIC state has to be
>     saved/restored.
> 
> vINTC state save/restore plumbing (patches 10-11)
>   - vintc_state_{save,restore}() wrappers over new store/restore hooks in
>     struct vintc_ops, and the vAPLIC implementation of those hooks. No
>     callers are wired up yet; the context-switch calls arrive with vCPU
>     context switch support.
> 
> Trap and instruction emulation infrastructure (patches 12-17)
>   - Extend the exception-table format with type/data fields and add
>     EX_TYPE_TRAP_INFO so fixups can capture sepc/scause/stval.
>   - riscv_vcpu_unpriv_read() (HLV/HLVX) to read guest memory/instructions
>     safely, and riscv_vcpu_trap_redirect() to forward a synchronous trap
>     back into the guest's VS-mode handler.
>   - A guest page-fault handler that decodes the trapped load/store
>     instruction (HTINST, or an unprivileged fetch as a fallback) and
>     dispatches the MMIO access through try_handle_mmio().
> 
> Note on versioning: the series is posted as v1 as a freshly split-out
> series, but several patches carry v2/v3 changelogs because they were
> previously circulated as part of a larger another patches [1] from which the
> current depends.
> 
> CI tests: 
> https://gitlab.com/xen-project/people/olkur/xen/-/pipelines/2690874319
> 
> [1] 
> https://lore.kernel.org/xen-devel/cover.1784559209.git.oleksii.kurochko@xxxxxxxxx/T/#t
> 
> Oleksii Kurochko (17):
>   xen/riscv: manage IRQ_DISABLED flag in APLIC irq enable/disable
>     callbacks
>   xen/riscv: add basic VGEIN management for AIA guests
>   xen/riscv: add missing APLIC register offsets, masks to asm/aplic.h
>   xen/riscv: introduce device-agnostic MMIO emulation dispatch
>   xen/riscv: implement virtual APLIC MMIO emulation
>   xen/riscv: map IMSIC interrupt file for vCPUs
>   xen/riscv: introduce vCPU AIA initialization
>   xen/riscv: add IMSIC state save/restore
>   xen/riscv: add helper to check APLIC MSI mode
>   xen/riscv: introduce vintc_state_{save,restore}()
>   xen/riscv: add vAPLIC state save/restore hooks
>   xen/riscv: extend exception tables with type and data fields
>   xen/riscv: add unprivileged guest memory read helper
>   xen/riscv: add guest page fault handling stub
>   xen/riscv: implement trap redirection to a guest
>   xen/riscv: add guest load emulation for trapped MMIO accesses
>   xen/riscv: add guest store emulation for trapped MMIO accesses

Where did the last two patches go? My inbox agrees with [1] that only 15 of the
17 patches arrived.

Jan

[1] https://lists.xen.org/archives/html/xen-devel/2026-07/threads.html