BACKPORT: arm/arm64: KVM: Statically configure the host's view of MPIDR

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. This patch is a part of KVM PMU patchset to fix the overflow issue (pmu-mem-access, pmu-chain-promotion, pmu-overflow-interrupt) in CentOS 8.0 This patch is backported from: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.10-rc6&id=32f139551954512bfdf9d558341af453bb8b12b4 Signed-off-by: Marc Zyngier <[email protected]> Acked-by: Christoffer Dall <[email protected]> Signed-off-by: Christoffer Dall <[email protected]> Signed-off-by: Khuong Dinh <[email protected]>
AmpereComputing · Jan 4, 2021 · 095370f · 095370f
1 parent 09efa20
commit 095370f
Show file tree

Hide file tree

Showing 5 changed files with 17 additions and 2 deletions.
diff --git 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
@@ -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
@@ -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
@@ -382,6 +383,13 @@ 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
@@ -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
@@ -1503,6 +1503,7 @@ 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) {