unimore/kernel-hacking-2024-linux-steffo
unimore/kernel-hacking-2024-linux-steffo
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irqchip/gic-v4: Substitute vmovp_lock for a per-VM lock

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vmovp_lock is abused in a number of cases to serialise updates
to vlpi_count[] and deal with map/unmap of a VM to ITSs.

Instead, provide a per-VM lock and revisit the use of vlpi_count[]
so that it is always wrapped in this per-VM vmapp_lock.

This reduces the potential contention on a concurrent VMOVP command,
and paves the way for subsequent VPE locking that holding vmovp_lock
actively prevents due to the lock ordering.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nianyao Tang <tangnianyao@huawei.com>
Link: https://lore.kernel.org/r/20240705093155.871070-3-maz@kernel.org
This commit is contained in:
Marc Zyngier 2024-07-05 10:31:54 +01:00 committed by Thomas Gleixner
parent 7d2c2048a8
commit f0eb154c39
2 changed files with 20 additions and 15 deletions
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27
drivers/irqchip/irq-gic-v3-its.c
View file

@ -1317,7 +1317,6 @@ static void its_send_vmovp(struct its_vpe *vpe)
{
struct its_cmd_desc desc = {};
struct its_node *its;
unsigned long flags;
int col_id = vpe->col_idx;
desc.its_vmovp_cmd.vpe = vpe;
@ -1329,6 +1328,12 @@ static void its_send_vmovp(struct its_vpe *vpe)
return;
}
/*
* Protect against concurrent updates of the mapping state on
* individual VMs.
*/
guard(raw_spinlock_irqsave)(&vpe->its_vm->vmapp_lock);
/*
* Yet another marvel of the architecture. If using the
* its_list "feature", we need to make sure that all ITSs
@ -1337,8 +1342,7 @@ static void its_send_vmovp(struct its_vpe *vpe)
*
* Wall <-- Head.
*/
raw_spin_lock_irqsave(&vmovp_lock, flags);
guard(raw_spinlock)(&vmovp_lock);
desc.its_vmovp_cmd.seq_num = vmovp_seq_num++;
desc.its_vmovp_cmd.its_list = get_its_list(vpe->its_vm);
@ -1353,8 +1357,6 @@ static void its_send_vmovp(struct its_vpe *vpe)
desc.its_vmovp_cmd.col = &its->collections[col_id];
its_send_single_vcommand(its, its_build_vmovp_cmd, &desc);
}
raw_spin_unlock_irqrestore(&vmovp_lock, flags);
}
static void its_send_vinvall(struct its_node *its, struct its_vpe *vpe)
@ -1791,12 +1793,10 @@ static bool gic_requires_eager_mapping(void)
static void its_map_vm(struct its_node *its, struct its_vm *vm)
{
unsigned long flags;
if (gic_requires_eager_mapping())
return;
raw_spin_lock_irqsave(&vmovp_lock, flags);
guard(raw_spinlock_irqsave)(&vm->vmapp_lock);
/*
* If the VM wasn't mapped yet, iterate over the vpes and get
@ -1814,19 +1814,15 @@ static void its_map_vm(struct its_node *its, struct its_vm *vm)
its_send_vinvall(its, vpe);
}
}
raw_spin_unlock_irqrestore(&vmovp_lock, flags);
}
static void its_unmap_vm(struct its_node *its, struct its_vm *vm)
{
unsigned long flags;
/* Not using the ITS list? Everything is always mapped. */
if (gic_requires_eager_mapping())
return;
raw_spin_lock_irqsave(&vmovp_lock, flags);
guard(raw_spinlock_irqsave)(&vm->vmapp_lock);
if (!--vm->vlpi_count[its->list_nr]) {
int i;
@ -1834,8 +1830,6 @@ static void its_unmap_vm(struct its_node *its, struct its_vm *vm)
for (i = 0; i < vm->nr_vpes; i++)
its_send_vmapp(its, vm->vpes[i], false);
}
raw_spin_unlock_irqrestore(&vmovp_lock, flags);
}
static int its_vlpi_map(struct irq_data *d, struct its_cmd_info *info)
@ -3942,6 +3936,8 @@ static void its_vpe_invall(struct its_vpe *vpe)
{
struct its_node *its;
guard(raw_spinlock_irqsave)(&vpe->its_vm->vmapp_lock);
list_for_each_entry(its, &its_nodes, entry) {
if (!is_v4(its))
continue;
@ -4547,6 +4543,7 @@ static int its_vpe_irq_domain_alloc(struct irq_domain *domain, unsigned int virq
vm->db_lpi_base = base;
vm->nr_db_lpis = nr_ids;
vm->vprop_page = vprop_page;
raw_spin_lock_init(&vm->vmapp_lock);
if (gic_rdists->has_rvpeid)
irqchip = &its_vpe_4_1_irq_chip;

8
include/linux/irqchip/arm-gic-v4.h
View file

@ -25,6 +25,14 @@ struct its_vm {
irq_hw_number_t db_lpi_base;
unsigned long *db_bitmap;
int nr_db_lpis;
/*
* Ensures mutual exclusion between updates to vlpi_count[]
* and map/unmap when using the ITSList mechanism.
*
* The lock order for any sequence involving the ITSList is
* vmapp_lock -> vpe_lock ->vmovp_lock.
*/
raw_spinlock_t vmapp_lock;
u32 vlpi_count[GICv4_ITS_LIST_MAX];
};