Re: [PATCH v8 3/5] xen/riscv: look up the exception table for any trap taken in Xen context

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 10/26/26 4:14 PM, Baptiste Le Duc wrote:
> From: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
>
> do_trap() consulted the exception table only for CAUSE_ILLEGAL_INSTRUCTION,
> which covers csr_read_safe() but not a probing access faulting with a page
> fault cause: it would reach do_unexpected_trap() instead of its fixup.
> There is no such access yet, the A/D update scheme probe will be the first.
>
> Move the lookup ahead of the cause switch, and only do it for exceptions
> taken in Xen context. Both other cases must skip it:
>
> - Traps taken from the guest: sepc is then a guest address, which the
>    guest can point at an address listed in the exception table, making Xen
>    act on an entry fully under guest control. Entries are matched by exact
>    address, so this needs no more than a numerical collision.
Nit: Identations here and ..

> - Interrupts: an interrupt taken at an address listed in the table would
>    otherwise be "fixed up" as if the access itself had faulted, silently
>    skipping it.
... looks incorrect a little bit. An extra space should be dropped.

> Returning early skips check_for_pcpu_work(), which is correct: that only
> runs for traps taken from the guest.
>
> Cache the "trap came from the guest" test in a local as it is now used
> three times.
>
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> [Baptiste: drop the parts depending on the vAPLIC/vIMSIC series, adapt
>   the commit message]
> Assisted-by: Claude:claude-opus-5-5
> Signed-off-by: Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>
> ---
> Changes since v7:
> - new patch, needed by the A/D update scheme probe of the next patch,
>    whose store page fault would otherwise not be fixed up. Taken from:
>    
> https://patch.msgid.link/4e2b4e7a99f4d2133ff92559303d19382749de7a.1790779209.git.oleksii.kurochko@xxxxxxxxx
> - commit message adapted to this subset: drop the hlv/hlvx and
>    EX_TYPE_TRAP_INFO parts and the paragraph on the guest page fault
>    BUG_ON(), whose code isn't taken; mention the from_guest local, which
>    this subset introduces.
> - apply my v3 review suggestion to the commit message: state up front
>    that the lookup is only done for exceptions taken in Xen context and
>    list traps taken from the guest and interrupts as the skipped cases.
> ---
LGTM:

Reviewed-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

~ Oleksii