On Wed, May 20, 2020 at 04:47:11PM +0100, Catalin Marinas wrote: > On Wed, May 20, 2020 at 01:20:13PM +0100, Will Deacon wrote: > > On Wed, May 20, 2020 at 06:52:54AM +0530, Anshuman Khandual wrote: > > > There is no way to proceed when requested register could not be searched > > > in > > > arm64_ftr_reg[]. Requesting for a non present register would be an error > > > as > > > well. Hence lets just BUG_ON() when the search fails in > > > get_arm64_ftr_reg() > > > rather than checking for return value and doing the same in some > > > individual > > > callers. > > > > > > But there are some callers that dont BUG_ON() upon search failure. It adds > > > an argument 'failsafe' that provides required switch between callers based > > > on whether they could proceed or not. > > > > > > Cc: Catalin Marinas <[email protected]> > > > Cc: Will Deacon <[email protected]> > > > Cc: Suzuki K Poulose <[email protected]> > > > Cc: Mark Brown <[email protected]> > > > Cc: [email protected] > > > Cc: [email protected] > > > > > > Signed-off-by: Anshuman Khandual <[email protected]> > > > --- > > > Applies on next-20200518 that has recent cpufeature changes from Will. > > > > > > arch/arm64/kernel/cpufeature.c | 26 +++++++++++++------------- > > > 1 file changed, 13 insertions(+), 13 deletions(-) > > > > > > diff --git a/arch/arm64/kernel/cpufeature.c > > > b/arch/arm64/kernel/cpufeature.c > > > index bc5048f152c1..62767cc540c3 100644 > > > --- a/arch/arm64/kernel/cpufeature.c > > > +++ b/arch/arm64/kernel/cpufeature.c > > > @@ -557,7 +557,7 @@ static int search_cmp_ftr_reg(const void *id, const > > > void *regp) > > > * - NULL on failure. It is upto the caller to decide > > > * the impact of a failure. > > > */ > > > -static struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id) > > > +static struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id, bool failsafe) > > > > Generally, I'm not a big fan of boolean arguments because they are really > > opaque at the callsite. It also seems bogus to me that we don't trust the > > caller to pass a valid sys_id, but we trust it to get "failsafe" right, > > which seems to mean "I promise to check the result isn't NULL before > > dereferencing it." > > > > So I don't see how this patch improves anything. I'd actually be more > > inclined to stick a WARN() in get_arm64_ftr_reg() when it returns NULL and > > have the callers handle NULL by returning early, getting rid of all the > > BUG_ONs in here. Sure, the system might end up in a funny state, but we > > WARN()d about it and tried to keep going (and Linus has some strong opinions > > on this too). > > Such WARN can be triggered by the user via emulate_sys_reg(), so we > can't really have it in get_arm64_ftr_reg() without a 'failsafe' option.
Ah yes, that would be bad. In which case, I don't think the existing code should change. Will
