[PATCH v8 1/4] arm/arm64: KVM: Add KVM_GET/SET_VCPU_EVENTS

[peter.maydell@linaro.org (Peter Maydell)]

On 19 July 2018 at 15:15, James Morse <james.morse@arm.com> wrote:
> Hi guys,
>
> On 19/07/18 08:39, gengdongjiu wrote:
>> On 2018/7/18 0:33, Peter Maydell wrote:
>>> On 13 July 2018 at 16:47, James Morse <james.morse@arm.com> wrote:
>>>> From: Dongjiu Geng <gengdongjiu@huawei.com>
>>>>
>>>> For the migrating VMs, user space may need to know the exception
>>>> state. For example, in the machine A, KVM make an SError pending,
>>>> when migrate to B, KVM also needs to pend an SError.
>>>>
>>>> This new IOCTL exports user-invisible states related to SError.
>>>> Together with appropriate user space changes, user space can get/set
>>>> the SError exception state to do migrate/snapshot/suspend.
>
>>>> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
>>>> index d10944e619d3..e3940f8715a5 100644
>>>> --- a/Documentation/virtual/kvm/api.txt
>>>> +++ b/Documentation/virtual/kvm/api.txt
>
>
>>>> +Gets currently pending SError exceptions as well as related states of the vcpu.
>>>
>>> Any chance of expanding this to explain what this state actually is?
>>> (ie something you could use to implement or review the userspace
>>> code which has to manipulate it)
>> sure, can expand it.
>>
>> serror_pending means whether KVM is pending Serror for guest.
>> serror_has_esr means whether KVM or user space can set the SError syndrome for guest.
>> serror_esr means the value of SError syndrome.
>
> I've had a go at something more verbose for this section:
> ------------------%<------------------
> If the guest accesses a device that is being emulated by the host kernel in such
> a way that a real device would generate a physical SError, KVM may make a
> virtual SError pending for that VCPU. This system error interrupt remains
> pending until the guest takes the exception by unmasking PSTATE.A.
>
> Running the VCPU may cause it to take a pending SError, or make an access that
> causes an SError to become pending. The event's description is only valid while
> the VPCU is not running.
>
> This API provides a way to read and write the pending 'event' state that is not
> visible to the guest. To save, restore or migrate a VCPU the struct representing
> the state can be read then written using this GET/SET API, along with the other
> guest-visible registers. It is not possible to 'cancel' an SError that has been
> made pending.
>
> A device being emulated in user-space may also wish to generate an SError. To do
> this the events structure can be populated by user-space. The current state
> should be read first, to ensure no existing SError is pending. If an existing
> SError is pending, the architectures 'Multiple SError interrupts' rules should

"architecture's"

> be followed. (2.5.3 of DDI0587.a "ARM Reliability, Availability, and
> Serviceability (RAS) Specification").
> ------------------%<------------------

Otherwise looks good.

thanks
-- PMM