On Tue, Sep 08, 2020 at 04:12:49PM +0200, Andrey Konovalov wrote: > On Tue, Sep 8, 2020 at 4:06 PM Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > On Tue, Sep 08, 2020 at 03:18:04PM +0200, Andrey Konovalov wrote: > > > On Thu, Aug 27, 2020 at 12:40 PM Catalin Marinas > > > <catalin.marinas@xxxxxxx> wrote: > > > > On Fri, Aug 14, 2020 at 07:27:08PM +0200, Andrey Konovalov wrote: > > > > > diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S > > > > > index 152d74f2cc9c..6880ddaa5144 100644 > > > > > --- a/arch/arm64/mm/proc.S > > > > > +++ b/arch/arm64/mm/proc.S > > > > > @@ -38,7 +38,7 @@ > > > > > /* PTWs cacheable, inner/outer WBWA */ > > > > > #define TCR_CACHE_FLAGS TCR_IRGN_WBWA | TCR_ORGN_WBWA > > > > > > > > > > -#ifdef CONFIG_KASAN_SW_TAGS > > > > > +#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS) > > > > > #define TCR_KASAN_FLAGS TCR_TBI1 > > > > > #else > > > > > #define TCR_KASAN_FLAGS 0 > > > > > > > > I prefer to turn TBI1 on only if MTE is present. So on top of the v8 > > > > user series, just do this in __cpu_setup. > > > > > > Started working on this, but realized that I don't understand what > > > exactly is suggested here. TCR_KASAN_FLAGS are used in __cpu_setup(), > > > so this already happens in __cpu_setup(). > > > > > > Do you mean that TBI1 should be enabled when CONFIG_ARM64_MTE is > > > enabled, but CONFIG_KASAN_HW_TAGS is disabled? > > > > What I meant is that we should turn TBI1 only when the MTE is present in > > hardware (and the ARM64_MTE option is on). But I probably missed the way > > MTE is used with KASAN. > > > > So what happens if CONFIG_KASAN_HW_TAGS and CONFIG_ARM64_MTE are both on > > but the hardware does not support MTE? Does KASAN still generate tagged > > pointers? If yes, then the current patch is fine, we should always set > > TBI1. > > No, the tag is always 0xFF when MTE is not supported. > > Should we then only enable TBI1 if system_supports_mte() or something > like that? You could add it do this block in __cpu_setup: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/tree/arch/arm64/mm/proc.S?h=for-next/mte#n429 It needs a few changes to have "mov_q x10, TCR_..." before the MTE check so that you can add the TBI1 bit in there. system_supports_mte() would be called too late, you want this set before the MMU is turned on. -- Catalin
