Commit 21f27df8 authored by Nico Boehr's avatar Nico Boehr Committed by Janosch Frank

KVM: s390: pv: fix external interruption loop not always detected

To determine whether the guest has caused an external interruption loop
upon code 20 (external interrupt) intercepts, the ext_new_psw needs to
be inspected to see whether external interrupts are enabled.

Under non-PV, ext_new_psw can simply be taken from guest lowcore. Under
PV, KVM can only access the encrypted guest lowcore and hence the
ext_new_psw must not be taken from guest lowcore.

handle_external_interrupt() incorrectly did that and hence was not able
to reliably tell whether an external interruption loop is happening or
not. False negatives cause spurious failures of my kvm-unit-test
for extint loops[1] under PV.

Since code 20 is only caused under PV if and only if the guest's
ext_new_psw is enabled for external interrupts, false positive detection
of a external interruption loop can not happen.

Fix this issue by instead looking at the guest PSW in the state
description. Since the PSW swap for external interrupt is done by the
ultravisor before the intercept is caused, this reliably tells whether
the guest is enabled for external interrupts in the ext_new_psw.

Also update the comments to explain better what is happening.

[1] https://lore.kernel.org/kvm/20220812062151.1980937-4-nrb@linux.ibm.com/Signed-off-by: default avatarNico Boehr <nrb@linux.ibm.com>
Reviewed-by: default avatarJanosch Frank <frankja@linux.ibm.com>
Reviewed-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Fixes: 201ae986 ("KVM: s390: protvirt: Implement interrupt injection")
Link: https://lore.kernel.org/r/20230213085520.100756-2-nrb@linux.ibm.com
Message-Id: <20230213085520.100756-2-nrb@linux.ibm.com>
Signed-off-by: default avatarJanosch Frank <frankja@linux.ibm.com>
parent 197b6b60
...@@ -271,10 +271,18 @@ static int handle_prog(struct kvm_vcpu *vcpu) ...@@ -271,10 +271,18 @@ static int handle_prog(struct kvm_vcpu *vcpu)
* handle_external_interrupt - used for external interruption interceptions * handle_external_interrupt - used for external interruption interceptions
* @vcpu: virtual cpu * @vcpu: virtual cpu
* *
* This interception only occurs if the CPUSTAT_EXT_INT bit was set, or if * This interception occurs if:
* the new PSW does not have external interrupts disabled. In the first case, * - the CPUSTAT_EXT_INT bit was already set when the external interrupt
* we've got to deliver the interrupt manually, and in the second case, we * occurred. In this case, the interrupt needs to be injected manually to
* drop to userspace to handle the situation there. * preserve interrupt priority.
* - the external new PSW has external interrupts enabled, which will cause an
* interruption loop. We drop to userspace in this case.
*
* The latter case can be detected by inspecting the external mask bit in the
* external new psw.
*
* Under PV, only the latter case can occur, since interrupt priorities are
* handled in the ultravisor.
*/ */
static int handle_external_interrupt(struct kvm_vcpu *vcpu) static int handle_external_interrupt(struct kvm_vcpu *vcpu)
{ {
...@@ -285,10 +293,18 @@ static int handle_external_interrupt(struct kvm_vcpu *vcpu) ...@@ -285,10 +293,18 @@ static int handle_external_interrupt(struct kvm_vcpu *vcpu)
vcpu->stat.exit_external_interrupt++; vcpu->stat.exit_external_interrupt++;
if (kvm_s390_pv_cpu_is_protected(vcpu)) {
newpsw = vcpu->arch.sie_block->gpsw;
} else {
rc = read_guest_lc(vcpu, __LC_EXT_NEW_PSW, &newpsw, sizeof(psw_t)); rc = read_guest_lc(vcpu, __LC_EXT_NEW_PSW, &newpsw, sizeof(psw_t));
if (rc) if (rc)
return rc; return rc;
/* We can not handle clock comparator or timer interrupt with bad PSW */ }
/*
* Clock comparator or timer interrupt with external interrupt enabled
* will cause interrupt loop. Drop to userspace.
*/
if ((eic == EXT_IRQ_CLK_COMP || eic == EXT_IRQ_CPU_TIMER) && if ((eic == EXT_IRQ_CLK_COMP || eic == EXT_IRQ_CPU_TIMER) &&
(newpsw.mask & PSW_MASK_EXT)) (newpsw.mask & PSW_MASK_EXT))
return -EOPNOTSUPP; return -EOPNOTSUPP;
......
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