Commit 2417218f authored by Oliver Upton's avatar Oliver Upton Committed by Marc Zyngier
Browse files

KVM: arm64: Get rid of __kvm_get_mdcr_el2() and related warts 



KVM caches MDCR_EL2 on a per-CPU basis in order to preserve the
configuration of MDCR_EL2.HPMN while running a guest. This is a bit
gross, since we're relying on some baked configuration rather than the
hardware definition of implemented counters.

Discover the number of implemented counters by reading PMCR_EL0.N
instead. This works because:

 - In VHE the kernel runs at EL2, and N always returns the number of
   counters implemented in hardware

 - In {n,h}VHE, the EL2 setup code programs MDCR_EL2.HPMN with the EL2
   view of PMCR_EL0.N for the host

Lastly, avoid traps under nested virtualization by saving PMCR_EL0.N in
host data.

Tested-by: default avatarJames Clark <james.clark@linaro.org>
Signed-off-by: default avatarOliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241219224116.3941496-3-oliver.upton@linux.dev


Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
parent 8ca19c40

arch/arm64/include/asm/kvm_asm.h

+1 −4
Original line number Diff line number Diff line
@@ -53,8 +53,7 @@ 
enum __kvm_host_smccc_func {

	/* Hypercalls available only prior to pKVM finalisation */

	/* __KVM_HOST_SMCCC_FUNC___kvm_hyp_init */

	__KVM_HOST_SMCCC_FUNC___kvm_get_mdcr_el2 = __KVM_HOST_SMCCC_FUNC___kvm_hyp_init + 1,

	__KVM_HOST_SMCCC_FUNC___pkvm_init,

	__KVM_HOST_SMCCC_FUNC___pkvm_init = __KVM_HOST_SMCCC_FUNC___kvm_hyp_init + 1,

	__KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping,

	__KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector,

	__KVM_HOST_SMCCC_FUNC___kvm_enable_ssbs,
@@ -247,8 +246,6 @@ extern void __kvm_adjust_pc(struct kvm_vcpu *vcpu); 
extern u64 __vgic_v3_get_gic_config(void);

extern void __vgic_v3_init_lrs(void);



extern u64 __kvm_get_mdcr_el2(void);



#define __KVM_EXTABLE(from, to)						\

	"	.pushsection	__kvm_ex_table, \"a\"\n"		\

	"	.align		3\n"					\

arch/arm64/include/asm/kvm_host.h

+5 −2
Original line number Diff line number Diff line
@@ -652,6 +652,9 @@ struct kvm_host_data { 
		/* Values of trap registers for the host before guest entry. */

		u64 mdcr_el2;

	} host_debug_state;



	/* Number of programmable event counters (PMCR_EL0.N) for this CPU */

	unsigned int nr_event_counters;

};



struct kvm_host_psci_config {
@@ -1332,7 +1335,7 @@ static inline bool kvm_system_needs_idmapped_vectors(void) 


static inline void kvm_arch_sync_events(struct kvm *kvm) {}



void kvm_arm_init_debug(void);

void kvm_init_host_debug_data(void);

void kvm_arm_vcpu_init_debug(struct kvm_vcpu *vcpu);

void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);

void kvm_arm_clear_debug(struct kvm_vcpu *vcpu);

arch/arm64/kvm/arm.c

+1 −1
Original line number Diff line number Diff line
@@ -2109,6 +2109,7 @@ static void cpu_set_hyp_vector(void) 
static void cpu_hyp_init_context(void)

{

	kvm_init_host_cpu_context(host_data_ptr(host_ctxt));

	kvm_init_host_debug_data();



	if (!is_kernel_in_hyp_mode())

		cpu_init_hyp_mode();
@@ -2117,7 +2118,6 @@ static void cpu_hyp_init_context(void) 
static void cpu_hyp_init_features(void)

{

	cpu_set_hyp_vector();

	kvm_arm_init_debug();



	if (is_kernel_in_hyp_mode())

		kvm_timer_init_vhe();

arch/arm64/kvm/debug.c

+11 −18
Original line number Diff line number Diff line
@@ -16,8 +16,6 @@ 


#include "trace.h"



static DEFINE_PER_CPU(u64, mdcr_el2);



/*

 * save/restore_guest_debug_regs

 *
@@ -60,21 +58,6 @@ static void restore_guest_debug_regs(struct kvm_vcpu *vcpu) 
		*vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;

}



/**

 * kvm_arm_init_debug - grab what we need for debug

 *

 * Currently the sole task of this function is to retrieve the initial

 * value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has

 * presumably been set-up by some knowledgeable bootcode.

 *

 * It is called once per-cpu during CPU hyp initialisation.

 */



void kvm_arm_init_debug(void)

{

	__this_cpu_write(mdcr_el2, kvm_call_hyp_ret(__kvm_get_mdcr_el2));

}



/**

 * kvm_arm_setup_mdcr_el2 - configure vcpu mdcr_el2 value

 *
@@ -94,7 +77,8 @@ static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu) 
	 * This also clears MDCR_EL2_E2PB_MASK and MDCR_EL2_E2TB_MASK

	 * to disable guest access to the profiling and trace buffers

	 */

	vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;

	vcpu->arch.mdcr_el2 = FIELD_PREP(MDCR_EL2_HPMN,

					 *host_data_ptr(nr_event_counters));

	vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |

				MDCR_EL2_TPMS |

				MDCR_EL2_TTRF |
@@ -338,3 +322,12 @@ void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu) 
	vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_SPE);

	vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRBE);

}



void kvm_init_host_debug_data(void)

{

	u64 dfr0 = read_sysreg(id_aa64dfr0_el1);



	if (cpuid_feature_extract_signed_field(dfr0, ID_AA64DFR0_EL1_PMUVer_SHIFT) > 0)

		*host_data_ptr(nr_event_counters) = FIELD_GET(ARMV8_PMU_PMCR_N,

							      read_sysreg(pmcr_el0));

}

arch/arm64/kvm/hyp/nvhe/debug-sr.c

+0 −5
Original line number Diff line number Diff line
@@ -106,8 +106,3 @@ void __debug_switch_to_host(struct kvm_vcpu *vcpu) 
{

	__debug_switch_to_host_common(vcpu);

}
 


u64 __kvm_get_mdcr_el2(void)

{

	return read_sysreg(mdcr_el2);

}