Re: [PATCH 1/4] KVM: arm64: Allow saving vgic3 LPI pending status in no running vcpu context

[Gavin Shan]

Hi Marc,

On 1/20/23 2:47 AM, Marc Zyngier wrote:
> On Thu, 19 Jan 2023 01:11:44 +0000,
> Gavin Shan <gshan@xxxxxxxxxx> wrote:
> > I will have vgic_write_guest_lock() in v2. Note that those 3 paths can't be
> > running in parallel since one switch is shared by them. Alternatively, we
> > extend struct vgic_dist::save_tables_in_progress from 'bool' to 'unsigned long'.
> > Several bit is defined for each site as below. In this way, the 3 paths can be
> > running in parallel:
> >
> >    unsigned long struct vgic_dist::save_tables_in_progress
> >
> >    #define VGIC_DIST_SAVE_ITS_ITE		0	/* ITS Translation Entry */
> >    #define VGIC_DIST_SAVE_ITS_DTE		1	/* ITS Device Table Entry */
> >    #define VGIC_DIST_SAVE_ITS_CTE		2	/* ITS Collection Table Entry */
> >    #define VGIC_DIST_SAVE_ITS_CT			3	/* ITS Collection Table */
> >    #define VGIC_DIST_SAVE_VGIC3_LPI		4	/* VGIC3 LPI Pending Status */
> >    #define VGIC_DIST_SAVE_VGIC3_PENDING_TABLE	5	/* VGIC3 Pending Table */
> >
> > The drawback is the calls are limited to 64. If those 3 paths can't be running
> > in parallel, we needn't the extension at all.
>
> It should all be completely sequential. KVM_DEV_ARM_ITS_SAVE_TABLES
> runs in a context where everything is locked, and so is
> VGIC_DIST_SAVE_VGIC3_PENDING_TABLE.

Thanks for your confirm. Yeah, it's sequential because 'kvm->lock' is
hold on KVM_DEV_ARM_ITS_SAVE_TABLES and VGIC_DIST_SAVE_VGIC3_PENDING_TABLE.
So all good to have one shared switch. v2 will be posted pretty soon.

Thanks,
Gavin