KVM: arm64: Honor trap routing for FPMR

HCRX_EL2.EnFPM controls the trapping of FPMR (as well as the validity
of any FP8 instruction, but we don't really care about this last part).

Describe the trap bit so that the exception can be reinjected in a
NV guest.

Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240820131802.3547589-6-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Marc Zyngier

arch/arm64/kvm/emulate-nested.c

@@ -83,6 +83,7 @@ enum cgt_group_id {
 	CGT_CPTR_TAM,
 	CGT_CPTR_TCPAC,
 
+	CGT_HCRX_EnFPM,
 	CGT_HCRX_TCR2En,
 
 	/*
@@ -372,6 +373,12 @@ static const struct trap_bits coarse_trap_bits[] = {
 		.mask		= CPTR_EL2_TCPAC,
 		.behaviour	= BEHAVE_FORWARD_ANY,
 	},
+	[CGT_HCRX_EnFPM] = {
+		.index		= HCRX_EL2,
+		.value 		= 0,
+		.mask		= HCRX_EL2_EnFPM,
+		.behaviour	= BEHAVE_FORWARD_ANY,
+	},
 	[CGT_HCRX_TCR2En] = {
 		.index		= HCRX_EL2,
 		.value 		= 0,
@@ -1108,6 +1115,7 @@ static const struct encoding_to_trap_config encoding_to_cgt[] __initconst = {
 	SR_TRAP(SYS_CNTP_CTL_EL0,	CGT_CNTHCTL_EL1PTEN),
 	SR_TRAP(SYS_CNTPCT_EL0,		CGT_CNTHCTL_EL1PCTEN),
 	SR_TRAP(SYS_CNTPCTSS_EL0,	CGT_CNTHCTL_EL1PCTEN),
+	SR_TRAP(SYS_FPMR,		CGT_HCRX_EnFPM),
 };
 
 static DEFINE_XARRAY(sr_forward_xa);