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

Browse source 
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: James Clark <james.clark@linaro.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241219224116.3941496-3-oliver.upton@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Oliver Upton 2024-12-19 14:40:59 -08:00 • committed by Marc Zyngier
parent 8ca19c40c4
commit 2417218f2f
7 changed files with 18 additions and 41 deletions
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5
arch/arm64/include/asm/kvm_asm.h
View file

@ -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" \

7
arch/arm64/include/asm/kvm_host.h
View file

@ -642,7 +642,7 @@ struct kvm_host_data {
* host_debug_state contains the host registers which are
* saved and restored during world switches.
*/
struct {
struct {
/* {Break,watch}point registers */
struct kvm_guest_debug_arch regs;
/* Statistical profiling extension */
@ -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);

2
arch/arm64/kvm/arm.c
View file

@ -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();

29
arch/arm64/kvm/debug.c
View file

@ -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));
}

5
arch/arm64/kvm/hyp/nvhe/debug-sr.c
View file

@ -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);
}

6
arch/arm64/kvm/hyp/nvhe/hyp-main.c
View file

@ -264,11 +264,6 @@ static void handle___vgic_v3_init_lrs(struct kvm_cpu_context *host_ctxt)
__vgic_v3_init_lrs();
}
static void handle___kvm_get_mdcr_el2(struct kvm_cpu_context *host_ctxt)
{
cpu_reg(host_ctxt, 1) = __kvm_get_mdcr_el2();
}
static void handle___vgic_v3_save_vmcr_aprs(struct kvm_cpu_context *host_ctxt)
{
DECLARE_REG(struct vgic_v3_cpu_if *, cpu_if, host_ctxt, 1);
@ -384,7 +379,6 @@ typedef void (*hcall_t)(struct kvm_cpu_context *);
static const hcall_t host_hcall[] = {
/* ___kvm_hyp_init */
HANDLE_FUNC(__kvm_get_mdcr_el2),
HANDLE_FUNC(__pkvm_init),
HANDLE_FUNC(__pkvm_create_private_mapping),
HANDLE_FUNC(__pkvm_cpu_set_vector),

5
arch/arm64/kvm/hyp/vhe/debug-sr.c
View file

@ -19,8 +19,3 @@ 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);
}