[PATCH 05/14] arm/arm64: KVM: Statically configure the host's view of MPIDR

Christoffer Dall
2019-01-24T14:00:23Z

From: Marc Zyngier <marc.zyngier@arm.com>

We currently eagerly save/restore MPIDR. It turns out to be
slightly pointless:
- On the host, this value is known as soon as we're scheduled on a
physical CPU
- In the guest, this value cannot change, as it is set by KVM
(and this is a read-only register)

The result of the above is that we can perfectly avoid the eager
saving of MPIDR_EL1, and only keep the restore. We just have
to setup the host contexts appropriately at boot time.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Christoffer Dall <christoffer.dall@arm.com>
---
arch/arm/include/asm/kvm_host.h | 8 ++++++++
arch/arm/kvm/hyp/cp15-sr.c | 1 -
arch/arm64/include/asm/kvm_host.h | 8 ++++++++
arch/arm64/kvm/hyp/sysreg-sr.c | 1 -
virt/kvm/arm/arm.c | 1 +
5 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 4b6193f2f0f6..43e343e00fb8 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -26,6 +26,7 @@
#include <asm/kvm_asm.h>
#include <asm/kvm_mmio.h>
#include <asm/fpstate.h>
+#include <asm/smp_plat.h>
#include <kvm/arm_arch_timer.h>

#define __KVM_HAVE_ARCH_INTC_INITIALIZED
@@ -147,6 +148,13 @@ struct kvm_cpu_context {

typedef struct kvm_cpu_context kvm_cpu_context_t;

+static inline void kvm_init_host_cpu_context(kvm_cpu_context_t *cpu_ctxt,
+ int cpu)
+{
+ /* The host's MPIDR is immutable, so let's set it up at boot time */
+ cpu_ctxt->cp15[c0_MPIDR] = cpu_logical_map(cpu);
+}
+
struct kvm_vcpu_arch {
struct kvm_cpu_context ctxt;

diff --git a/arch/arm/kvm/hyp/cp15-sr.c b/arch/arm/kvm/hyp/cp15-sr.c
index c4782812714c..8bf895ec6e04 100644
--- a/arch/arm/kvm/hyp/cp15-sr.c
+++ b/arch/arm/kvm/hyp/cp15-sr.c
@@ -27,7 +27,6 @@ static u64 *cp15_64(struct kvm_cpu_context *ctxt, int idx)

void __hyp_text __sysreg_save_state(struct kvm_cpu_context *ctxt)
{
- ctxt->cp15[c0_MPIDR] = read_sysreg(VMPIDR);
ctxt->cp15[c0_CSSELR] = read_sysreg(CSSELR);
ctxt->cp15[c1_SCTLR] = read_sysreg(SCTLR);
ctxt->cp15[c1_CPACR] = read_sysreg(CPACR);
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 8b7702bdb219..f497bb31031f 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -30,6 +30,7 @@
#include <asm/kvm.h>
#include <asm/kvm_asm.h>
#include <asm/kvm_mmio.h>
+#include <asm/smp_plat.h>
#include <asm/thread_info.h>

#define __KVM_HAVE_ARCH_INTC_INITIALIZED
@@ -418,6 +419,13 @@ struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);

DECLARE_PER_CPU(kvm_cpu_context_t, kvm_host_cpu_state);

+static inline void kvm_init_host_cpu_context(kvm_cpu_context_t *cpu_ctxt,
+ int cpu)
+{
+ /* The host's MPIDR is immutable, so let's set it up at boot time */
+ cpu_ctxt->sys_regs[MPIDR_EL1] = cpu_logical_map(cpu);
+}
+
void __kvm_enable_ssbs(void);

static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
index 68d6f7c3b237..2498f86defcb 100644
--- a/arch/arm64/kvm/hyp/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/sysreg-sr.c
@@ -52,7 +52,6 @@ static void __hyp_text __sysreg_save_user_state(struct kvm_cpu_context *ctxt)

static void __hyp_text __sysreg_save_el1_state(struct kvm_cpu_context *ctxt)
{
- ctxt->sys_regs[MPIDR_EL1] = read_sysreg(vmpidr_el2);
ctxt->sys_regs[CSSELR_EL1] = read_sysreg(csselr_el1);
ctxt->sys_regs[SCTLR_EL1] = read_sysreg_el1(sctlr);
ctxt->sys_regs[ACTLR_EL1] = read_sysreg(actlr_el1);
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 4d55f98f97f7..3dd240ea9e76 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -1561,6 +1561,7 @@ static int init_hyp_mode(void)
kvm_cpu_context_t *cpu_ctxt;

cpu_ctxt = per_cpu_ptr(&kvm_host_cpu_state, cpu);
+ kvm_init_host_cpu_context(cpu_ctxt, cpu);
err = create_hyp_mappings(cpu_ctxt, cpu_ctxt + 1, PAGE_HYP);

if (err) {
--
2.18.0