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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 08, 2020 at 07:24:12PM +0100, Vincenzo Frascino wrote: > On 10/2/20 3:06 PM, Catalin Marinas wrote: > > On Fri, Oct 02, 2020 at 01:10:30AM +0200, Andrey Konovalov wrote: > >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > >> index 7c67ac6f08df..d1847f29f59b 100644 > >> --- a/arch/arm64/kernel/mte.c > >> +++ b/arch/arm64/kernel/mte.c > >> @@ -23,6 +23,8 @@ > >> #include > >> #include > >> > >> +u64 gcr_kernel_excl __ro_after_init; > >> + > >> static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > >> { > >> pte_t old_pte = READ_ONCE(*ptep); > >> @@ -120,6 +122,13 @@ void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag) > >> return ptr; > >> } > >> > >> +void mte_init_tags(u64 max_tag) > >> +{ > >> + u64 incl = GENMASK(max_tag & MTE_TAG_MAX, 0); > > > > Nitpick: it's not obvious that MTE_TAG_MAX is a mask, so better write > > this as GENMASK(min(max_tag, MTE_TAG_MAX), 0). > > The two things do not seem equivalent because the format of the tags in KASAN is > 0xFF and in MTE is 0xF, hence if extract the minimum whatever is the tag passed > by KASAN it will always be MTE_TAG_MAX. > > To make it cleaner I propose: GENMASK(FIELD_GET(MTE_TAG_MAX, max_tag), 0); I don't think that's any clearer since FIELD_GET still assumes that MTE_TAG_MAX is a mask. I think it's better to add a comment on why this is needed, as you explained above that the KASAN tags go to 0xff. If you want to get rid of MTE_TAG_MAX altogether, just do a max_tag &= (1 << MAX_TAG_SIZE) - 1; before setting incl (a comment is still useful). -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel