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KVM: arm64: Evaluate debug owner at vcpu_load()

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In preparation for tossing the debug_ptr mess, introduce an enumeration
to track the ownership of the debug registers while in the guest. Update
the owner at vcpu_load() based on whether the host needs to steal the
guest's debug context or if breakpoints/watchpoints are actively in use.

Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241219224116.3941496-7-oliver.upton@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Oliver Upton
2024-12-19 14:41:03 -08:00
committed by Marc Zyngier
parent b47ffd13fd
commit cd9b10102a
4 changed files with 60 additions and 0 deletions
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11
arch/arm64/include/asm/kvm_host.h
View File

@@ -756,6 +756,12 @@ struct kvm_vcpu_arch {
struct kvm_guest_debug_arch vcpu_debug_state;
struct kvm_guest_debug_arch external_debug_state;
enum {
VCPU_DEBUG_FREE,
VCPU_DEBUG_HOST_OWNED,
VCPU_DEBUG_GUEST_OWNED,
} debug_owner;
/* VGIC state */
struct vgic_cpu vgic_cpu;
struct arch_timer_cpu timer_cpu;
@@ -1345,10 +1351,15 @@ 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);
void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu);
void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu);
void kvm_debug_set_guest_ownership(struct kvm_vcpu *vcpu);
#define kvm_vcpu_os_lock_enabled(vcpu) \
(!!(__vcpu_sys_reg(vcpu, OSLSR_EL1) & OSLSR_EL1_OSLK))
#define kvm_host_owns_debug_regs(vcpu) \
((vcpu)->arch.debug_owner == VCPU_DEBUG_HOST_OWNED)
int kvm_arm_vcpu_arch_set_attr(struct kvm_vcpu *vcpu,
struct kvm_device_attr *attr);
int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu,

1
arch/arm64/kvm/arm.c
View File

@@ -598,6 +598,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
kvm_vgic_load(vcpu);
kvm_timer_vcpu_load(vcpu);
kvm_vcpu_load_debug(vcpu);
if (has_vhe())
kvm_vcpu_load_vhe(vcpu);
kvm_arch_vcpu_load_fp(vcpu);

46
arch/arm64/kvm/debug.c
View File

@@ -317,3 +317,49 @@ void kvm_init_host_debug_data(void)
!(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_EL1_P))
host_data_set_flag(HAS_TRBE);
}
void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu)
{
u64 mdscr;
/* Must be called before kvm_vcpu_load_vhe() */
KVM_BUG_ON(vcpu_get_flag(vcpu, SYSREGS_ON_CPU), vcpu->kvm);
/*
* Determine which of the possible debug states we're in:
*
* - VCPU_DEBUG_HOST_OWNED: KVM has taken ownership of the guest's
* breakpoint/watchpoint registers, or needs to use MDSCR_EL1 to do
* software step or emulate the effects of the OS Lock being enabled.
*
* - VCPU_DEBUG_GUEST_OWNED: The guest has debug exceptions enabled, and
* the breakpoint/watchpoint registers need to be loaded eagerly.
*
* - VCPU_DEBUG_FREE: Neither of the above apply, no breakpoint/watchpoint
* context needs to be loaded on the CPU.
*/
if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
vcpu->arch.debug_owner = VCPU_DEBUG_HOST_OWNED;
} else {
mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
if (mdscr & (MDSCR_EL1_KDE | MDSCR_EL1_MDE))
vcpu->arch.debug_owner = VCPU_DEBUG_GUEST_OWNED;
else
vcpu->arch.debug_owner = VCPU_DEBUG_FREE;
}
}
/*
* Updates ownership of the debug registers after a trapped guest access to a
* breakpoint/watchpoint register. Host ownership of the debug registers is of
* strictly higher priority, and it is the responsibility of the VMM to emulate
* guest debug exceptions in this configuration.
*/
void kvm_debug_set_guest_ownership(struct kvm_vcpu *vcpu)
{
if (kvm_host_owns_debug_regs(vcpu))
return;
vcpu->arch.debug_owner = VCPU_DEBUG_GUEST_OWNED;
}

2
arch/arm64/kvm/sys_regs.c
View File

@@ -656,6 +656,7 @@ static bool trap_debug_regs(struct kvm_vcpu *vcpu,
if (p->is_write)
vcpu_set_flag(vcpu, DEBUG_DIRTY);
kvm_debug_set_guest_ownership(vcpu);
trace_trap_reg(__func__, r->reg, p->is_write, p->regval);
return true;
@@ -684,6 +685,7 @@ static void reg_to_dbg(struct kvm_vcpu *vcpu,
val |= (p->regval & (mask >> shift)) << shift;
*dbg_reg = val;
kvm_debug_set_guest_ownership(vcpu);
vcpu_set_flag(vcpu, DEBUG_DIRTY);
}