Commit cd9b1010 authored by Oliver Upton's avatar Oliver Upton Committed by Marc Zyngier
Browse files

KVM: arm64: Evaluate debug owner at vcpu_load() 



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: default avatarJames Clark <james.clark@linaro.org>
Signed-off-by: default avatarOliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241219224116.3941496-7-oliver.upton@linux.dev


Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
parent b47ffd13

arch/arm64/include/asm/kvm_host.h

+11 −0
Original line number Diff line number Diff line
@@ -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,

arch/arm64/kvm/arm.c

+1 −0
Original line number Diff line number Diff line
@@ -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);

arch/arm64/kvm/debug.c

+46 −0
Original line number Diff line number Diff line
@@ -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;

}

arch/arm64/kvm/sys_regs.c

+2 −0
Original line number Diff line number Diff line
@@ -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);

}