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KVM: arm64: nv: Publish emulated timer interrupt state in the in-memory state

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With FEAT_NV2, the EL0 timer state is entirely stored in memory,
meaning that the hypervisor can only provide a very poor emulation.

The only thing we can really do is to publish the interrupt state
in the guest view of CNT{P,V}_CTL_EL0, and defer everything else
to the next exit.

Only FEAT_ECV will allow us to fix it, at the cost of extra trapping.

Suggested-by: Chase Conklin <chase.conklin@arm.com>
Suggested-by: Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>
Acked-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241217142321.763801-4-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Marc Zyngier 2024-12-17 14:23:11 +00:00
parent 4bad3068cf
commit cc45963cbf
2 changed files with 22 additions and 1 deletions
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21
arch/arm64/kvm/arch_timer.c
View file

@ -441,11 +441,30 @@ void kvm_timer_update_run(struct kvm_vcpu *vcpu)
regs->device_irq_level |= KVM_ARM_DEV_EL1_PTIMER;
}
static void kvm_timer_update_status(struct arch_timer_context *ctx, bool level)
{
/*
* Paper over NV2 brokenness by publishing the interrupt status
* bit. This still results in a poor quality of emulation (guest
* writes will have no effect until the next exit).
*
* But hey, it's fast, right?
*/
if (is_hyp_ctxt(ctx->vcpu) &&
(ctx == vcpu_vtimer(ctx->vcpu) || ctx == vcpu_ptimer(ctx->vcpu))) {
unsigned long val = timer_get_ctl(ctx);
__assign_bit(__ffs(ARCH_TIMER_CTRL_IT_STAT), &val, level);
timer_set_ctl(ctx, val);
}
}
static void kvm_timer_update_irq(struct kvm_vcpu *vcpu, bool new_level,
struct arch_timer_context *timer_ctx)
{
int ret;
kvm_timer_update_status(timer_ctx, new_level);
timer_ctx->irq.level = new_level;
trace_kvm_timer_update_irq(vcpu->vcpu_id, timer_irq(timer_ctx),
timer_ctx->irq.level);
@ -471,6 +490,8 @@ static void timer_emulate(struct arch_timer_context *ctx)
return;
}
kvm_timer_update_status(ctx, should_fire);
/*
* If the timer can fire now, we don't need to have a soft timer
* scheduled for the future. If the timer cannot fire at all,

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

@ -1228,7 +1228,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
if (unlikely(!irqchip_in_kernel(vcpu->kvm)))
kvm_timer_sync_user(vcpu);
if (vcpu_has_nv(vcpu))
if (is_hyp_ctxt(vcpu))
kvm_timer_sync_nested(vcpu);
kvm_arch_vcpu_ctxsync_fp(vcpu);