[PATCH 1/6] arm64: Add MT_S2{,_FWB}_AS_S1 encodings

[Marc Zyngier <maz@kernel.org>]

pKVM usage of S2 translation on the host is purely for isolation
purposes, not translation. To that effect, the memory attributes
being used must be that of S1.

With FWB=0, this is easily achieved by using the Normal Cacheable
type (which is the weakest possible memory type) at S2, and let S1
pick something stronger as required.

With FWB=1, the attributes are combined in a different way, and we
cannot arbitrarily use Normal Cacheable. We can, however, use a
memattr encoding that indicates that the final attributes are that
of Stage-1.

Add these encoding and a few pointers to the relevant parts of the
specification. It might come handy some day.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/memory.h | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 9d54b2ea49d66..a2b7a33966ff1 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -175,19 +175,24 @@
 #define MT_DEVICE_nGnRE		4
 
 /*
- * Memory types for Stage-2 translation
+ * Memory types for Stage-2 translation when HCR_EL2.FWB=0. See R_HMNDG,
+ * R_TNHFM, R_GQFSF and I_MCQKW for the details on how these attributes get
+ * combined with Stage-1.
  */
 #define MT_S2_NORMAL		0xf
 #define MT_S2_NORMAL_NC		0x5
 #define MT_S2_DEVICE_nGnRE	0x1
+#define MT_S2_AS_S1		MT_S2_NORMAL
 
 /*
- * Memory types for Stage-2 translation when ID_AA64MMFR2_EL1.FWB is 0001
- * Stage-2 enforces Normal-WB and Device-nGnRE
+ * Memory types for Stage-2 translation when HCR_EL2.FWB=1. Stage-2 enforces
+ * Normal-WB and Device-nGnRE, unless we actively say that S1 wins. See
+ * R_VRJSW and R_RHWZM for details.
  */
 #define MT_S2_FWB_NORMAL	6
 #define MT_S2_FWB_NORMAL_NC	5
 #define MT_S2_FWB_DEVICE_nGnRE	1
+#define MT_S2_FWB_AS_S1		7
 
 #ifdef CONFIG_ARM64_4K_PAGES
 #define IOREMAP_MAX_ORDER	(PUD_SHIFT)
-- 
2.47.3