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

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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




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