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Re: [PATCH v3 25/39] xen/riscv: add guest store emulation for trapped MMIO accesses
- To: Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>
- From: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- Date: Wed, 4 Nov 2026 17:51:17 +0100
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Romain Caritey <Romain.Caritey@xxxxxxxxxxxxx>, Zheng Zhang <zhangzheng@xxxxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger@xxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- Delivery-date: Wed, 04 Nov 2026 16:51:28 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10/22/26 2:37 PM, Baptiste Le Duc wrote:
Extend the guest page fault handler with store emulation to support MMIO
write accesses.
Like emulate_load(), emulate_store() obtains the trapped instruction with
insn_fetch_faulted(), which also deals with a fault taken while re-reading
it, and decodes it with decode_ldst_insn(). As with the load path, the
access is completed synchronously through do_mmio().
At the moment only virtual interrupt controller (vINTC) traps are expected
to occur, since it is currently the only backend registered with the MMIO
handler dispatch, so in practice the store is emulated via the vINTC
backend.
Nit: the wording is unclear because "emulated via the vINTC backend" sounds
like the vINTC does the decoding, I'd suggest:
```
At the moment the only MMIO handler registered is the vAPLIC one, so in
practice every trapped guest store ends up in vaplic_mmio_ops' write
handler.
```
Instead of that,
Good suggestion, it is really better!
everything LGTM, so:
Reviewed-by: Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>
Thanks!
~ Oleksii
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