Re: [PATCH v1 01/24] LoongArch: KVM: Implement kvm module related interface

[Tianrui Zhao]

在 2023年02月17日 03:34, Oliver Upton 写道:
> On Tue, Feb 14, 2023 at 09:00:50PM +0800, Tianrui Zhao wrote:
> > 在 2023年02月14日 17:58, Greg Kroah-Hartman 写道:
> > > On Tue, Feb 14, 2023 at 05:00:56PM +0800, Tianrui Zhao wrote:
> > > > > > +#define KVM_GET_CSRS		_IOWR(KVMIO, 0xc5, struct kvm_csrs)
> > > > > > +#define KVM_SET_CSRS		_IOW(KVMIO,  0xc6, struct kvm_csrs)
> > > > > Why does this arch need new ioctls?
> > > > We want to use this ioctl to access multiple csrs at one time. If without
> > > > this, we only access one csr.
> > > What is wrong with accessing only one csr at a time?  Isn't this what
> > > other architectures do?
> > Generally, using KVM_GET_ONE_GET ioctl to get one reg, but we want a
> > more convenient interface to get serial regs at one time, so we add this
> > ioctl.
> Have you found register accesses through the KVM_{GET,SET}_ONE_REG
> ioctls to actually be a bounding issue? I'd be surprised if that were
> actually the case.
>
> An architecture-neutral implementation was entertained a few years ago
> [*], but even then it saved an inconsequential amount of time relative
> to the rest of VM serialization (at least for arm64). The one thing that
> series got right was to share the plumbing across all architectures that
> use the ONE_REG interface (i.e. everyone but x86).
>
> If you have data that supports the thesis that a batched ioctl is
> useful then please do share. But in any case this should not use an ioctl
> tied down to a single architecture.
>
> [*] https://lore.kernel.org/kvm/20201120125616.14436-1-darkhan@xxxxxxxxxx/

Thanks for your explanation, and we have decided to remove this ioctls.

thanks,
Tianrui Zhao