On 19 July 2018 at 15:15, James Morse <james.morse@xxxxxxx> 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@xxxxxxx> wrote: >>>> From: Dongjiu Geng <gengdongjiu@xxxxxxxxxx> >>>> >>>> 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
