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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.10.2026 16:26, Oleksii Kurochko wrote:
> 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.

Things are indeed off-by-1 in your reply, but in Baptiste's original mail
all looks fine.

>> 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>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan