On Mon, Jul 01, 2024 at 10:54:58AM +0100, Steven Price wrote: > When __change_memory_common() is purely setting the valid bit on a PTE > (e.g. via the set_memory_valid() call) there is no need for a TLBI as > either the entry isn't changing (the valid bit was already set) or the > entry was invalid and so should not have been cached in the TLB. > > Signed-off-by: Steven Price <steven.price@xxxxxxx> > --- > v4: New patch > --- > arch/arm64/mm/pageattr.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c > index 0e270a1c51e6..547a9e0b46c2 100644 > --- a/arch/arm64/mm/pageattr.c > +++ b/arch/arm64/mm/pageattr.c > @@ -60,7 +60,13 @@ static int __change_memory_common(unsigned long start, unsigned long size, > ret = apply_to_page_range(&init_mm, start, size, change_page_range, > &data); > > - flush_tlb_kernel_range(start, start + size); > + /* > + * If the memory is being made valid without changing any other bits > + * then a TLBI isn't required as a non-valid entry cannot be cached in > + * the TLB. > + */ > + if (pgprot_val(set_mask) != PTE_VALID || pgprot_val(clear_mask)) > + flush_tlb_kernel_range(start, start + size); > return ret; Can you elaborate on when this actually happens, please? It feels like a case of "Doctor, it hurts when I do this" rather than something we should be trying to short-circuit in the low-level code. Will
