[RFC 5/8] KVM: arm64: Explicitly handle MDSELR_EL1 traps as UNDEFINED

[Anshuman Khandual]

Currently read_sanitised_id_aa64dfr0_el1() caps the ID_AA64DFR0.DebugVer to
ID_AA64DFR0_DebugVer_V8P8, resulting in FEAT_Debugv8p9 not being exposed to
the guest. MDSELR_EL1 register access in the guest, is currently trapped by
the existing configuration of the fine-grained traps.

As the register is not described in sys_reg_descs[] table emulate_sys_reg()
will warn that this is unknown access before injecting an UNDEFINED
exception into the guest. Any well-behaved guests shouldn't try to use this
register, but any badly-behaved guests could, thus resulting in unnecessary
warnings. To avoid such warnings, access to MDSELR_EL1 should be explicitly
handled as UNDEFINED via updating sys_reg_desc[] as required.

Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Oliver Upton <oliver.upton@xxxxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: kvmarm@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
---
 arch/arm64/kvm/sys_regs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index c9f4f387155f..2956bdcd358e 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2203,6 +2203,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ SYS_DESC(SYS_MDSCR_EL1), trap_debug_regs, reset_val, MDSCR_EL1, 0 },
 	DBG_BCR_BVR_WCR_WVR_EL1(2),
 	DBG_BCR_BVR_WCR_WVR_EL1(3),
+	{ SYS_DESC(SYS_MDSELR_EL1), undef_access },
 	DBG_BCR_BVR_WCR_WVR_EL1(4),
 	DBG_BCR_BVR_WCR_WVR_EL1(5),
 	DBG_BCR_BVR_WCR_WVR_EL1(6),
-- 
2.25.1