KVM: PPC: Book3S PR: Emulate PURR, SPURR and DSCR registers

This adds basic emulation of the PURR and SPURR registers. We assume
we are emulating a single-threaded core, so these advance at the same
rate as the timebase. A Linux kernel running on a POWER7 expects to
be able to access these registers and is not prepared to handle a
program interrupt on accessing them.

This also adds a very minimal emulation of the DSCR (data stream
control register). Writes are ignored and reads return zero.

Signed-off-by: Paul Mackerras <[e-mail]>
Signed-off-by: Alexander Graf <[e-mail]>

arch/powerpc/include/asm/kvm_book3s.h

···
 	u64 sdr1;
 	u64 hior;
 	u64 msr_mask;
+	u64 purr_offset;
+	u64 spurr_offset;
 #ifdef CONFIG_PPC_BOOK3S_32
 	u32 vsid_pool[VSID_POOL_SIZE];
 	u32 vsid_next;

arch/powerpc/kvm/book3s_emulate.c

···
 #include <asm/kvm_book3s.h>
 #include <asm/reg.h>
 #include <asm/switch_to.h>
+#include <asm/time.h>
 
 #define OP_19_XOP_RFID		18
 #define OP_19_XOP_RFI		50
···
 		    (mfmsr() & MSR_HV))
 			vcpu->arch.hflags |= BOOK3S_HFLAG_DCBZ32;
 		break;
+	case SPRN_PURR:
+		to_book3s(vcpu)->purr_offset = spr_val - get_tb();
+		break;
+	case SPRN_SPURR:
+		to_book3s(vcpu)->spurr_offset = spr_val - get_tb();
+		break;
 	case SPRN_GQR0:
 	case SPRN_GQR1:
 	case SPRN_GQR2:
···
 	case SPRN_CTRLF:
 	case SPRN_CTRLT:
 	case SPRN_L2CR:
+	case SPRN_DSCR:
 	case SPRN_MMCR0_GEKKO:
 	case SPRN_MMCR1_GEKKO:
 	case SPRN_PMC1_GEKKO:
···
 		*spr_val = to_book3s(vcpu)->hid[5];
 		break;
 	case SPRN_CFAR:
-	case SPRN_PURR:
+	case SPRN_DSCR:
 		*spr_val = 0;
+		break;
+	case SPRN_PURR:
+		*spr_val = get_tb() + to_book3s(vcpu)->purr_offset;
+		break;
+	case SPRN_SPURR:
+		*spr_val = get_tb() + to_book3s(vcpu)->purr_offset;
 		break;
 	case SPRN_GQR0:
 	case SPRN_GQR1: