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irqchip/gic-v3-its: Fix GICv4.1 VPE affinity update

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When updating the affinity of a VPE, the VMOVP command is currently skipped
if the two CPUs are part of the same VPE affinity.

But this is wrong, as the doorbell corresponding to this VPE is still
delivered on the 'old' CPU, which screws up the balancing.  Furthermore,
offlining that 'old' CPU results in doorbell interrupts generated for this
VPE being discarded.

The harsh reality is that VMOVP cannot be elided when a set_affinity()
request occurs. It needs to be obeyed, and if an optimisation is to be
made, it is at the point where the affinity change request is made (such as
in KVM).

Drop the VMOVP elision altogether, and only use the vpe_table_mask
to try and stay within the same ITS affinity group if at all possible.

Fixes: dd3f050a21 (irqchip/gic-v4.1: Implement the v4.1 flavour of VMOVP)
Reported-by: Kunkun Jiang <jiangkunkun@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240213101206.2137483-4-maz@kernel.org
This commit is contained in:
Marc Zyngier 2024-02-13 10:12:06 +00:00 committed by Thomas Gleixner
parent 8b02da04ad
commit af9acbfc2c
1 changed files with 13 additions and 9 deletions
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22
drivers/irqchip/irq-gic-v3-its.c
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@ -3826,8 +3826,9 @@ static int its_vpe_set_affinity(struct irq_data *d,
bool force)
{
struct its_vpe *vpe = irq_data_get_irq_chip_data(d);
int from, cpu = cpumask_first(mask_val);
struct cpumask common, *table_mask;
unsigned long flags;
int from, cpu;
/*
* Changing affinity is mega expensive, so let's be as lazy as
@ -3843,19 +3844,22 @@ static int its_vpe_set_affinity(struct irq_data *d,
* taken on any vLPI handling path that evaluates vpe->col_idx.
*/
from = vpe_to_cpuid_lock(vpe, &flags);
table_mask = gic_data_rdist_cpu(from)->vpe_table_mask;
/*
* If we are offered another CPU in the same GICv4.1 ITS
* affinity, pick this one. Otherwise, any CPU will do.
*/
if (table_mask && cpumask_and(&common, mask_val, table_mask))
cpu = cpumask_test_cpu(from, &common) ? from : cpumask_first(&common);
else
cpu = cpumask_first(mask_val);
if (from == cpu)
goto out;
vpe->col_idx = cpu;
/*
* GICv4.1 allows us to skip VMOVP if moving to a cpu whose RD
* is sharing its VPE table with the current one.
*/
if (gic_data_rdist_cpu(cpu)->vpe_table_mask &&
cpumask_test_cpu(from, gic_data_rdist_cpu(cpu)->vpe_table_mask))
goto out;
its_send_vmovp(vpe);
its_vpe_db_proxy_move(vpe, from, cpu);