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SubjectRe: [PATCH v2 12/36] irqchip/gic-v4.1: Implement the v4.1 flavour of VMAPP
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Hi Marc,

On 2019/10/27 22:42, Marc Zyngier wrote:
> The ITS VMAPP command gains some new fields with GICv4.1:
> - a default doorbell, which allows a single doorbell to be used for
> all the VLPIs routed to a given VPE
> - a pointer to the configuration table (instead of having it in a register
> that gets context switched)
> - a flag indicating whether this is the first map or the last unmap for
> this particulat VPE
> - a flag indicating whether the pending table is known to be zeroed, or not
>
> Plumb in the new fields in the VMAPP builder, and add the map/unmap
> refcounting so that the ITS can do the right thing.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>

[...]

> @@ -605,19 +626,45 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
> struct its_cmd_block *cmd,
> struct its_cmd_desc *desc)
> {
> - unsigned long vpt_addr;
> + unsigned long vpt_addr, vconf_addr;
> u64 target;
> -
> - vpt_addr = virt_to_phys(page_address(desc->its_vmapp_cmd.vpe->vpt_page));
> - target = desc->its_vmapp_cmd.col->target_address + its->vlpi_redist_offset;
> + bool alloc;
>
> its_encode_cmd(cmd, GITS_CMD_VMAPP);
> its_encode_vpeid(cmd, desc->its_vmapp_cmd.vpe->vpe_id);
> its_encode_valid(cmd, desc->its_vmapp_cmd.valid);
> +
> + if (!desc->its_vmapp_cmd.valid) {
> + if (is_v4_1(its)) {
> + alloc = !atomic_dec_return(&desc->its_vmapp_cmd.vpe->vmapp_count);
> + its_encode_alloc(cmd, alloc);
> + }
> +
> + goto out;
> + }
> +
> + vpt_addr = virt_to_phys(page_address(desc->its_vmapp_cmd.vpe->vpt_page));
> + target = desc->its_vmapp_cmd.col->target_address + its->vlpi_redist_offset;
> +
> its_encode_target(cmd, target);
> its_encode_vpt_addr(cmd, vpt_addr);
> its_encode_vpt_size(cmd, LPI_NRBITS - 1);
>
> + if (!is_v4_1(its))
> + goto out;
> +
> + vconf_addr = virt_to_phys(page_address(desc->its_vmapp_cmd.vpe->its_vm->vprop_page));
> +
> + alloc = atomic_inc_and_test(&desc->its_vmapp_cmd.vpe->vmapp_count);

As the comment block on top of atomic_inc_and_test(atomic *v) says,

* Atomically increments @v by 1
* and returns true if the result is zero, or false for all
* other cases.
*/

We will always get the 'alloc' as false here, even if this is the
first mapping of this vPE. This is not as expected, I think.

And on the other hand, I wonder what is the reason for 'vmapp_count'
to be atomic_t?


Thanks,
Zenghui

> +
> + its_encode_alloc(cmd, alloc);
> +
> + /* We can only signal PTZ when alloc==1. Why do we have two bits? */
> + its_encode_ptz(cmd, alloc);
> + its_encode_vconf_addr(cmd, vconf_addr);
> + its_encode_vmapp_default_db(cmd, desc->its_vmapp_cmd.vpe->vpe_db_lpi);
> +
> +out:
> its_fixup_cmd(cmd);
>
> return valid_vpe(its, desc->its_vmapp_cmd.vpe);
> @@ -3349,7 +3396,10 @@ static int its_vpe_init(struct its_vpe *vpe)
>
> vpe->vpe_id = vpe_id;
> vpe->vpt_page = vpt_page;
> - vpe->vpe_proxy_event = -1;
> + if (gic_rdists->has_rvpeid)
> + atomic_set(&vpe->vmapp_count, 0);
> + else
> + vpe->vpe_proxy_event = -1;
>
> return 0;
> }
> diff --git a/include/linux/irqchip/arm-gic-v4.h b/include/linux/irqchip/arm-gic-v4.h
> index ab1396afe08a..6213ced6f199 100644
> --- a/include/linux/irqchip/arm-gic-v4.h
> +++ b/include/linux/irqchip/arm-gic-v4.h
> @@ -37,8 +37,20 @@ struct its_vpe {
> irq_hw_number_t vpe_db_lpi;
> /* VPE resident */
> bool resident;
> - /* VPE proxy mapping */
> - int vpe_proxy_event;
> + union {
> + /* GICv4.0 implementations */
> + struct {
> + /* VPE proxy mapping */
> + int vpe_proxy_event;
> + /* Implementation Defined Area Invalid */
> + bool idai;
> + };
> + /* GICv4.1 implementations */
> + struct {
> + atomic_t vmapp_count;
> + };
> + };
> +
> /*
> * This collection ID is used to indirect the target
> * redistributor for this VPE. The ID itself isn't involved in
> @@ -47,8 +59,6 @@ struct its_vpe {
> u16 col_idx;
> /* Unique (system-wide) VPE identifier */
> u16 vpe_id;
> - /* Implementation Defined Area Invalid */
> - bool idai;
> /* Pending VLPIs on schedule out? */
> bool pending_last;
> };
>

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