On Tue, Sep 08, 2020 at 03:23:20PM +0200, Andrey Konovalov wrote:

On Thu, Aug 27, 2020 at 11:38 AM Catalin Marinas
[off-list ref] wrote:

quoted

On Fri, Aug 14, 2020 at 07:27:02PM +0200, Andrey Konovalov wrote:

quoted

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 1c99fcadb58c..733be1cb5c95 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h

@@ -5,14 +5,19 @@
 #ifndef __ASM_MTE_H
 #define __ASM_MTE_H

-#define MTE_GRANULE_SIZE     UL(16)
+#include <asm/mte_asm.h>

So the reason for this move is to include it in asm/cache.h. Fine by
me but...

quoted

 #define MTE_GRANULE_MASK     (~(MTE_GRANULE_SIZE - 1))
 #define MTE_TAG_SHIFT                56
 #define MTE_TAG_SIZE         4
+#define MTE_TAG_MASK         GENMASK((MTE_TAG_SHIFT + (MTE_TAG_SIZE - 1)), MTE_TAG_SHIFT)
+#define MTE_TAG_MAX          (MTE_TAG_MASK >> MTE_TAG_SHIFT)

... I'd rather move all these definitions in a file with a more
meaningful name like mte-def.h. The _asm implies being meant for .S
files inclusion which isn't the case.

quoted

diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index eb39504e390a..e2d708b4583d 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c

@@ -72,6 +74,47 @@ int memcmp_pages(struct page *page1, struct page *page2)
      return ret;
 }

+u8 mte_get_mem_tag(void *addr)
+{
+     if (system_supports_mte())
+             addr = mte_assign_valid_ptr_tag(addr);

The mte_assign_valid_ptr_tag() is slightly misleading. All it does is
read the allocation tag from memory.

I also think this should be inline asm, possibly using alternatives.
It's just an LDG instruction (and it saves us from having to invent a
better function name).

Could you point me to an example of inline asm with alternatives if
there's any? I see alternative_if and other similar macros used in
arch/arm64/ code, is that what you mean? Those seem to always use
static conditions, like config values, but here we have a dynamic
system_supports_mte(). Could you elaborate on how I should implement
this?

There are plenty of ALTERNATIVE macro uses under arch/arm64, see
arch/arm64/include/asm/alternative.h for the definition and some simple
documentation.

In this case, something like (untested, haven't even checked whether it
matches the mte_assign_valid_ptr_tag() code):

	asm(ALTERNATIVE("orr %0, %1, #0xff << 56", "ldg %0, [%1]", ARM64_HAS_MTE));

-- 
Catalin

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