KVM: arm64: Add RES1_WHEN_E2Hx constraints as configuration flags

"Thanks" to VHE, SCTLR_EL2 radically changes shape depending on the
value of HCR_EL2.E2H, as a lot of the bits that didn't have much
meaning with E2H=0 start impacting EL0 with E2H=1.

This has a direct impact on the RESx behaviour of these bits, and
we need a way to express them.

For this purpose, introduce two new constaints that, when the
controlling feature is not present, force the field to RES1 depending
on the value of E2H. Note that RES0 is still implicit,

This allows diverging RESx values depending on the value of E2H,
something that is required by a bunch of SCTLR_EL2 bits.

Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-13-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Marc Zyngier

arch/arm64/kvm/config.c

@@ -26,6 +26,8 @@ struct reg_bits_to_feat_map {
 #define	MASKS_POINTER	BIT(3)	/* Pointer to fgt_masks struct instead of bits */
 #define	AS_RES1		BIT(4)	/* RES1 when not supported */
 #define	REQUIRES_E2H1	BIT(5)	/* Add HCR_EL2.E2H RES1 as a pre-condition */
+#define	RES1_WHEN_E2H0	BIT(6)	/* RES1 when E2H=0 and not supported */
+#define	RES1_WHEN_E2H1	BIT(7)	/* RES1 when E2H=1 and not supported */
 
 	unsigned long	flags;
 
@@ -1297,10 +1299,14 @@ static struct resx compute_resx_bits(struct kvm *kvm,
 			match &= !e2h0;
 
 		if (!match) {
-			if (map[i].flags & AS_RES1)
-				resx.res1 |= reg_feat_map_bits(&map[i]);
+			u64 bits = reg_feat_map_bits(&map[i]);
+
+			if ((map[i].flags & AS_RES1)			||
+			    (e2h0 && (map[i].flags & RES1_WHEN_E2H0))	||
+			    (!e2h0 && (map[i].flags & RES1_WHEN_E2H1)))
+				resx.res1 |= bits;
 			else
-				resx.res0 |= reg_feat_map_bits(&map[i]);
+				resx.res0 |= bits;
 		}
 	}