Re: [æéäåèååéé] Re: [RFC PATCH] KVM: arm/arm64: vgic: change condition for level interrupt resampling

[Marc Zyngier]

On 08/03/18 09:31, Yang, Shunyong wrote:
> Hi, Eric,
> 
> First, please let me changeÂChristoffer's email toÂcdall@xxxxxxxxxxx I
> add more information about my test below, please check.
> 
> On Thu, 2018-03-08 at 09:57 +0100, Auger Eric wrote:
>> Hi,
>>
>> On 08/03/18 08:01, Shunyong Yang wrote:
>>>
>>> When resampling irqfds is enabled, level interrupt should be
>>> de-asserted when resampling happens. On page 4-47 of GIC v3
>>> specification IHI0069D, it said,
>>> "When the PE acknowledges an SGI, a PPI, or an SPI at the CPU
>>> interface, the IRI changes the status of the interrupt to active
>>> and pending if:
>>> â It is an edge-triggered interrupt, and another edge has been
>>> detected since the interrupt was acknowledged.
>>> â It is a level-sensitive interrupt, and the level has not been
>>> deasserted since the interrupt was acknowledged."
>>>
>>> GIC v2 specification IHI0048B.b has similar description on page
>>> 3-42 for state machine transition.
>>>
>>> When some VFIO device, like mtty(8250 VFIO mdev emulation driver
>>> in samples/vfio-mdev) triggers a level interrupt, the status
>>> transition in LR is pending-->active-->active and pending.
>>> Then it will wait resampling to de-assert the interrupt.
>>>
>>> Current design of lr_signals_eoi_mi() will return false if state
>>> in LR is not invalid(Inactive). It causes resampling will not
>>> happen
>>> in mtty case.
>>>
>>> This will cause interrupt fired continuously to guest even 8250 IIR
>>> has no interrupt. When 8250's interrupt is configured in shared
>>> mode,
>>> it will pass interrupt to other drivers to handle. However, there
>>> is no other driver involved. Then, a "nobody cared" kernel
>>> complaint
>>> occurs.
>>>
>>> / # cat /dev/ttyS0
>>> [ÂÂÂÂ4.826836] random: crng init done
>>> [ÂÂÂÂ6.373620] irq 41: nobody cared (try booting with the "irqpoll"
>>> option)
>>> [ÂÂÂÂ6.376414] CPU: 0 PID: 1307 Comm: cat Not tainted 4.16.0-rc4 #4
>>> [ÂÂÂÂ6.378927] Hardware name: linux,dummy-virt (DT)
>>> [ÂÂÂÂ6.380876] Call trace:
>>> [ÂÂÂÂ6.381937]ÂÂdump_backtrace+0x0/0x180
>>> [ÂÂÂÂ6.383495]ÂÂshow_stack+0x14/0x1c
>>> [ÂÂÂÂ6.384902]ÂÂdump_stack+0x90/0xb4
>>> [ÂÂÂÂ6.386312]ÂÂ__report_bad_irq+0x38/0xe0
>>> [ÂÂÂÂ6.387944]ÂÂnote_interrupt+0x1f4/0x2b8
>>> [ÂÂÂÂ6.389568]ÂÂhandle_irq_event_percpu+0x54/0x7c
>>> [ÂÂÂÂ6.391433]ÂÂhandle_irq_event+0x44/0x74
>>> [ÂÂÂÂ6.393056]ÂÂhandle_fasteoi_irq+0x9c/0x154
>>> [ÂÂÂÂ6.394784]ÂÂgeneric_handle_irq+0x24/0x38
>>> [ÂÂÂÂ6.396483]ÂÂ__handle_domain_irq+0x60/0xb4
>>> [ÂÂÂÂ6.398207]ÂÂgic_handle_irq+0x98/0x1b0
>>> [ÂÂÂÂ6.399796]ÂÂel1_irq+0xb0/0x128
>>> [ÂÂÂÂ6.401138]ÂÂ_raw_spin_unlock_irqrestore+0x18/0x40
>>> [ÂÂÂÂ6.403149]ÂÂ__setup_irq+0x41c/0x678
>>> [ÂÂÂÂ6.404669]ÂÂrequest_threaded_irq+0xe0/0x190
>>> [ÂÂÂÂ6.406474]ÂÂuniv8250_setup_irq+0x208/0x234
>>> [ÂÂÂÂ6.408250]ÂÂserial8250_do_startup+0x1b4/0x754
>>> [ÂÂÂÂ6.410123]ÂÂserial8250_startup+0x20/0x28
>>> [ÂÂÂÂ6.411826]ÂÂuart_startup.part.21+0x78/0x144
>>> [ÂÂÂÂ6.413633]ÂÂuart_port_activate+0x50/0x68
>>> [ÂÂÂÂ6.415328]ÂÂtty_port_open+0x84/0xd4
>>> [ÂÂÂÂ6.416851]ÂÂuart_open+0x34/0x44
>>> [ÂÂÂÂ6.418229]ÂÂtty_open+0xec/0x3c8
>>> [ÂÂÂÂ6.419610]ÂÂchrdev_open+0xb0/0x198
>>> [ÂÂÂÂ6.421093]ÂÂdo_dentry_open+0x200/0x310
>>> [ÂÂÂÂ6.422714]ÂÂvfs_open+0x54/0x84
>>> [ÂÂÂÂ6.424054]ÂÂpath_openat+0x2dc/0xf04
>>> [ÂÂÂÂ6.425569]ÂÂdo_filp_open+0x68/0xd8
>>> [ÂÂÂÂ6.427044]ÂÂdo_sys_open+0x16c/0x224
>>> [ÂÂÂÂ6.428563]ÂÂSyS_openat+0x10/0x18
>>> [ÂÂÂÂ6.429972]ÂÂel0_svc_naked+0x30/0x34
>>> [ÂÂÂÂ6.431494] handlers:
>>> [ÂÂÂÂ6.432479] [<000000000e9fb4bb>] serial8250_interrupt
>>> [ÂÂÂÂ6.434597] Disabling IRQ #41
>>>
>>> This patch changes the lr state condition in lr_signals_eoi_mi()
>>> from
>>> invalid(Inactive) to active and pending to avoid this.
>>>
>>> I am not sure about the original design of the condition of
>>> invalid(active). So, This RFC is sent out for comments.
>>>
>>> Cc: Joey Zheng <yu.zheng@xxxxxxxxxxxxxxxx>
>>> Signed-off-by: Shunyong Yang <shunyong.yang@xxxxxxxxxxxxxxxx>
>>> ---
>>> Âvirt/kvm/arm/vgic/vgic-v2.c | 4 ++--
>>> Âvirt/kvm/arm/vgic/vgic-v3.c | 4 ++--
>>> Â2 files changed, 4 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-
>>> v2.c
>>> index e9d840a75e7b..740ee9a5f551 100644
>>> --- a/virt/kvm/arm/vgic/vgic-v2.c
>>> +++ b/virt/kvm/arm/vgic/vgic-v2.c
>>> @@ -46,8 +46,8 @@ void vgic_v2_set_underflow(struct kvm_vcpu *vcpu)
>>> Â
>>> Âstatic bool lr_signals_eoi_mi(u32 lr_val)
>>> Â{
>>> -	return !(lr_val & GICH_LR_STATE) && (lr_val & GICH_LR_EOI)
>>> &&
>>> -	ÂÂÂÂÂÂÂ!(lr_val & GICH_LR_HW);
>>> +	return !((lr_val & GICH_LR_STATE) ^ GICH_LR_STATE) &&
>>> +	ÂÂÂÂÂÂÂ(lr_val & GICH_LR_EOI) && !(lr_val & GICH_LR_HW);
>>> Â}
>>> Â
>>> Â/*
>>> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-
>>> v3.c
>>> index 6b329414e57a..43111bba7af9 100644
>>> --- a/virt/kvm/arm/vgic/vgic-v3.c
>>> +++ b/virt/kvm/arm/vgic/vgic-v3.c
>>> @@ -35,8 +35,8 @@ void vgic_v3_set_underflow(struct kvm_vcpu *vcpu)
>>> Â
>>> Âstatic bool lr_signals_eoi_mi(u64 lr_val)
>>> Â{
>>> -	return !(lr_val & ICH_LR_STATE) && (lr_val & ICH_LR_EOI)
>>> &&
>>> -	ÂÂÂÂÂÂÂ!(lr_val & ICH_LR_HW);
>>> +	return !((lr_val & ICH_LR_STATE) ^ ICH_LR_STATE) &&
>>> +	ÂÂÂÂÂÂÂ(lr_val & ICH_LR_EOI) && !(lr_val & ICH_LR_HW);
>>
>> In general don't we have this state transition
>>
>> inactive -> pending -> pending + active (1) -> active -> inactive.
>>
>> In that case won't we lower the virt irq level when folding the LR on
>> Pending + Active state, which is not was we want?
>>
>> Thanks
>>
>> Eric
> 
> In current code, in my test, when I output LR value of the mtty IRQ 41
> (hwirq = 36) inÂvgic_v3_fold_lr_state(). The LR's transition starts
> like following,
> 
> 0-->50a0020000000024-->90a0020000000024-->d0a0020000000024
> 
> That is inactive-->pending-->active-->pending + active.
> Then it keep running cyclic pending-->active-->pending + active.
> 
> The level interrupt de-assert should happen in following code
> /* Notify fds when the guest EOI'ed a level-triggered IRQ */
> 	if (lr_signals_eoi_mi(val) && vgic_valid_spi(vcpu->kvm, intid))
> 		kvm_notify_acked_irq(vcpu->kvm, 0,
> 				ÂÂÂÂÂintid - VGIC_NR_PRIVATE_IRQS);
> 
> But as addressed in commit message, lr_signals_eoi_mi() will return
> false if state in LR is not invalid(inactive), so it has no chance to
> de-assert the level interrupt in my test. 

The problem is that pending+active is not an indication that the guest
has actually EOI'd anything. In only indicates that it has been activated.

Note that there is a bit of vocabulary discrepancy between KVM and the
ARM architecture: KVM uses "acked" where ARM uses EOI. ARM uses "ACK" or
"Activate" for something entirely different. Maybe the confusion stems
from this difference.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...