On Tue, Sep 8, 2020 at 4:06 PM Catalin Marinas [off-list ref] wrote:

On Tue, Sep 08, 2020 at 03:18:04PM +0200, Andrey Konovalov wrote:

quoted

On Thu, Aug 27, 2020 at 12:40 PM Catalin Marinas
[off-list ref] wrote:

quoted

On Fri, Aug 14, 2020 at 07:27:08PM +0200, Andrey Konovalov wrote:

quoted

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?

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