Re: [PATCH 1/4] arm64: signal: Preserve POR_EL0 if poe_context is missing

[Will Deacon <will@kernel.org>]

On Wed, Apr 22, 2026 at 04:55:05PM +0200, Kevin Brodsky wrote:
> On 22/04/2026 14:19, Will Deacon wrote:
> >> @@ -74,8 +76,12 @@ struct rt_sigframe_user_layout {
> >>   * This state needs to be carefully managed to ensure that it doesn't cause
> >>   * uaccess to fail when setting up the signal frame, and the signal handler
> >>   * itself also expects a well-defined state when entered.
> >> + *
> >> + * The valid_fields member is a bitfield (see UA_STATE_HAS_*), specifying which
> >> + * of the remaining fields is valid (has been set to a value).
> >>   */
> >>  struct user_access_state {
> >> +	unsigned int valid_fields;
> >>  	u64 por_el0;
> >>  };
> > Do you think it would be worth adding some accessors to make it easier
> > to keep the flags in sync? For example:
> >
> > /* Stores por_el0 into uas->por_el0 and sets UA_STATE_HAS_POR_EL0 */
> > void set_ua_state_por_el0(struct user_access_state *uas, u64 por_el0);
> >
> > /*
> >  * If UA_STATE_HAS_POR_EL0, *por_el0 = uas->por_el0 and return 0.
> >  * Otherwise, return -ENOENT.
> >  */
> > int get_ua_state_por_el0(struct user_access_state *uas, u64 *por_el0);
> >
> > WDYT?
> 
> I did get a feeling having helpers would be a good idea. I wonder if
> getters/setters aren't a bit overkill though, as they make accesses to
> the struct more cumbersome and we'd need a pair for every member (unless
> we use some macro magic).

We only have one struct member, so it's probably fine for now, and we
could group related members together in sub-structures to help in future.
But it's up to you -- I don't feel strongly about it, but requiring the
caller to update the flag manually is going to be a bug magnet.

> Maybe it would be sufficient to have say
> ua_state_has_field(POR_EL0) to check if the bit is set, and
> ua_state_set_field_valid(POR_EL0) to set the bit?

I don't think that really helps with my concern. I'd like to avoid callers
having to remember to deal with the flags when they update the data.

Will