[PATCH V2 11/14] KVM: MIPS: Add CPUCFG emulation for Loongson-3

Huacai Chen
2020-04-24T11:14:44Z

Loongson-3 overrides lwc2 instructions to implement CPUCFG and CSR
read/write functions. These instructions all cause guest exit so CSR
doesn't benifit KVM guest (and there are always legacy methods to
provide the same functions as CSR). So, we only emulate CPUCFG and let
it return 0 (which means the virtual CPU doesn't have any advanced
features, including CSR) in KVM.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Co-developed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
arch/mips/include/asm/kvm_host.h | 3 +++
arch/mips/include/uapi/asm/inst.h | 11 +++++++++
arch/mips/kvm/mips.c | 3 +++
arch/mips/kvm/vz.c | 50 +++++++++++++++++++++++++++++++++++++++
4 files changed, 67 insertions(+)

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index c98eb42..fa5fc86 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -173,6 +173,9 @@ struct kvm_vcpu_stat {
u64 vz_ghfc_exits;
u64 vz_gpa_exits;
u64 vz_resvd_exits;
+#ifdef CONFIG_CPU_LOONGSON64
+ u64 vz_cpucfg_exits;
+#endif
#endif
u64 halt_successful_poll;
u64 halt_attempted_poll;
diff --git a/arch/mips/include/uapi/asm/inst.h b/arch/mips/include/uapi/asm/inst.h
index 98f97c8..43d1faa 100644
--- a/arch/mips/include/uapi/asm/inst.h
+++ b/arch/mips/include/uapi/asm/inst.h
@@ -1012,6 +1012,16 @@ struct loongson3_lsdc2_format { /* Loongson-3 overridden ldc2/sdc2 Load/Store fo
;))))))
};

+struct loongson3_lscsr_format { /* Loongson-3 CPUCFG&CSR read/write format */
+ __BITFIELD_FIELD(unsigned int opcode : 6,
+ __BITFIELD_FIELD(unsigned int rs : 5,
+ __BITFIELD_FIELD(unsigned int fr : 5,
+ __BITFIELD_FIELD(unsigned int rd : 5,
+ __BITFIELD_FIELD(unsigned int fd : 5,
+ __BITFIELD_FIELD(unsigned int func : 6,
+ ;))))))
+};
+
/*
* MIPS16e instruction formats (16-bit length)
*/
@@ -1114,6 +1124,7 @@ union mips_instruction {
struct mm16_r5_format mm16_r5_format;
struct loongson3_lswc2_format loongson3_lswc2_format;
struct loongson3_lsdc2_format loongson3_lsdc2_format;
+ struct loongson3_lscsr_format loongson3_lscsr_format;
};

union mips16e_instruction {
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index ed989ef..9362769 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -68,6 +68,9 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
{ "vz_ghfc", VCPU_STAT(vz_ghfc_exits), KVM_STAT_VCPU },
{ "vz_gpa", VCPU_STAT(vz_gpa_exits), KVM_STAT_VCPU },
{ "vz_resvd", VCPU_STAT(vz_resvd_exits), KVM_STAT_VCPU },
+#ifdef CONFIG_CPU_LOONGSON64
+ { "vz_cpucfg", VCPU_STAT(vz_cpucfg_exits), KVM_STAT_VCPU },
+#endif
#endif
{ "halt_successful_poll", VCPU_STAT(halt_successful_poll), KVM_STAT_VCPU },
{ "halt_attempted_poll", VCPU_STAT(halt_attempted_poll), KVM_STAT_VCPU },
diff --git a/arch/mips/kvm/vz.c b/arch/mips/kvm/vz.c
index 63d5b35..cea1ce4 100644
--- a/arch/mips/kvm/vz.c
+++ b/arch/mips/kvm/vz.c
@@ -29,6 +29,7 @@
#include <linux/kvm_host.h>

#include "interrupt.h"
+#include "loongson_regs.h"

#include "trace.h"

@@ -1092,6 +1093,50 @@ static enum emulation_result kvm_vz_gpsi_cache(union mips_instruction inst,
return EMULATE_FAIL;
}

+#ifdef CONFIG_CPU_LOONGSON64
+static enum emulation_result kvm_vz_gpsi_lwc2(union mips_instruction inst,
+ u32 *opc, u32 cause,
+ struct kvm_run *run,
+ struct kvm_vcpu *vcpu)
+{
+ unsigned int rs, rd;
+ unsigned long curr_pc;
+ enum emulation_result er = EMULATE_DONE;
+
+ /*
+ * Update PC and hold onto current PC in case there is
+ * an error and we want to rollback the PC
+ */
+ curr_pc = vcpu->arch.pc;
+ er = update_pc(vcpu, cause);
+ if (er == EMULATE_FAIL)
+ return er;
+
+ rs = inst.loongson3_lscsr_format.rs;
+ rd = inst.loongson3_lscsr_format.rd;
+ switch (inst.loongson3_lscsr_format.fr) {
+ case 0x8: /* Read CPUCFG */
+ ++vcpu->stat.vz_cpucfg_exits;
+ vcpu->arch.gprs[rd] = 0; /* Don't export any advanced features to guest */
+ break;
+ default:
+ kvm_err("lwc2 emulate not impl %d rs %lx @%lx\n",
+ inst.loongson3_lscsr_format.fr, vcpu->arch.gprs[rs], curr_pc);
+ er = EMULATE_FAIL;
+ break;
+ }
+ /* Rollback PC only if emulation was unsuccessful */
+ if (er == EMULATE_FAIL) {
+ kvm_err("[%#lx]%s: unsupported lwc2 instruction 0x%08x 0x%08x\n",
+ curr_pc, __func__, inst.word, inst.loongson3_lscsr_format.fr);
+
+ vcpu->arch.pc = curr_pc;
+ }
+
+ return er;
+}
+#endif
+
static enum emulation_result kvm_trap_vz_handle_gpsi(u32 cause, u32 *opc,
struct kvm_vcpu *vcpu)
{
@@ -1121,6 +1166,11 @@ static enum emulation_result kvm_trap_vz_handle_gpsi(u32 cause, u32 *opc,
er = kvm_vz_gpsi_cache(inst, opc, cause, run, vcpu);
break;
#endif
+#ifdef CONFIG_CPU_LOONGSON64
+ case lwc2_op:
+ er = kvm_vz_gpsi_lwc2(inst, opc, cause, run, vcpu);
+ break;
+#endif
case spec3_op:
switch (inst.spec3_format.func) {
#ifdef CONFIG_CPU_MIPSR6
--
2.7.0