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KVM: arm64: Don't hijack guest context MDSCR_EL1

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Stealing MDSCR_EL1 in the guest's kvm_cpu_context for external debugging
is rather gross. Just add a field for this instead and let the context
switch code pick the correct one based on the debug owner.

Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241219224116.3941496-15-oliver.upton@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Oliver Upton
2024-12-19 14:41:11 -08:00
committed by Marc Zyngier
parent 75a5fbaf66
commit 4ad3a0b87f
3 changed files with 64 additions and 52 deletions
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75
arch/arm64/kvm/debug.c
View File

@@ -31,19 +31,12 @@
*/
static void save_guest_debug_regs(struct kvm_vcpu *vcpu)
{
u64 val = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
vcpu->arch.guest_debug_preserved.mdscr_el1 = val;
vcpu->arch.guest_debug_preserved.pstate_ss =
(*vcpu_cpsr(vcpu) & DBG_SPSR_SS);
}
static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
{
u64 val = vcpu->arch.guest_debug_preserved.mdscr_el1;
vcpu_write_sys_reg(vcpu, val, MDSCR_EL1);
if (vcpu->arch.guest_debug_preserved.pstate_ss)
*vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
else
@@ -115,8 +108,6 @@ static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
{
unsigned long mdscr;
/* Check if we need to use the debug registers. */
if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
/* Save guest debug state */
@@ -154,36 +145,6 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
*vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
else
*vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
mdscr |= DBG_MDSCR_SS;
vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
} else {
mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
mdscr &= ~DBG_MDSCR_SS;
vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
}
/*
* Enable breakpoints and watchpoints if userspace wants them.
*/
if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
mdscr |= DBG_MDSCR_MDE;
vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
/*
* The OS Lock blocks debug exceptions in all ELs when it is
* enabled. If the guest has enabled the OS Lock, constrain its
* effects to the guest. Emulate the behavior by clearing
* MDSCR_EL1.MDE. In so doing, we ensure that host debug
* exceptions are unaffected by guest configuration of the OS
* Lock.
*/
} else if (kvm_vcpu_os_lock_enabled(vcpu)) {
mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
mdscr &= ~DBG_MDSCR_MDE;
vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
}
}
}
@@ -227,6 +188,41 @@ void kvm_init_host_debug_data(void)
host_data_set_flag(HAS_TRBE);
}
/*
* Configures the 'external' MDSCR_EL1 value for the guest, i.e. when the host
* has taken over MDSCR_EL1.
*
* - Userspace is single-stepping the guest, and MDSCR_EL1.SS is forced to 1.
*
* - Userspace is using the breakpoint/watchpoint registers to debug the
* guest, and MDSCR_EL1.MDE is forced to 1.
*
* - The guest has enabled the OS Lock, and KVM is forcing MDSCR_EL1.MDE to 0,
* masking all debug exceptions affected by the OS Lock.
*/
static void setup_external_mdscr(struct kvm_vcpu *vcpu)
{
/*
* Use the guest's MDSCR_EL1 as a starting point, since there are
* several other features controlled by MDSCR_EL1 that are not relevant
* to the host.
*
* Clear the bits that KVM may use which also satisfies emulation of
* the OS Lock as MDSCR_EL1.MDE is cleared.
*/
u64 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1) & ~(MDSCR_EL1_SS |
MDSCR_EL1_MDE |
MDSCR_EL1_KDE);
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
mdscr |= MDSCR_EL1_SS;
if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW)
mdscr |= MDSCR_EL1_MDE | MDSCR_EL1_KDE;
vcpu->arch.external_mdscr_el1 = mdscr;
}
void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu)
{
u64 mdscr;
@@ -249,6 +245,7 @@ void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu)
*/
if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
vcpu->arch.debug_owner = VCPU_DEBUG_HOST_OWNED;
setup_external_mdscr(vcpu);
} else {
mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);