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

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 7/27/26 5:21 PM, Jan Beulich wrote:
> 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.
They lost for some reason, I sent them separately again. Now it should 
be okay.
> [1] https://lists.xen.org/archives/html/xen-devel/2026-07/threads.html