[PATCH 5.17 058/158] arm64: paravirt: Use RCU read locks to guard stolen_time

Greg Kroah-Hartman
2022-05-23T17:58:50Z

From: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>

commit 19bef63f951e47dd4ba54810e6f7c7ff9344a3ef upstream.

During hotplug, the stolen time data structure is unmapped and memset.
There is a possibility of the timer IRQ being triggered before memset
and stolen time is getting updated as part of this timer IRQ handler. This
causes the below crash in timer handler -

[ 3457.473139][ C5] Unable to handle kernel paging request at virtual address ffffffc03df05148
...
[ 3458.154398][ C5] Call trace:
[ 3458.157648][ C5] para_steal_clock+0x30/0x50
[ 3458.162319][ C5] irqtime_account_process_tick+0x30/0x194
[ 3458.168148][ C5] account_process_tick+0x3c/0x280
[ 3458.173274][ C5] update_process_times+0x5c/0xf4
[ 3458.178311][ C5] tick_sched_timer+0x180/0x384
[ 3458.183164][ C5] __run_hrtimer+0x160/0x57c
[ 3458.187744][ C5] hrtimer_interrupt+0x258/0x684
[ 3458.192698][ C5] arch_timer_handler_virt+0x5c/0xa0
[ 3458.198002][ C5] handle_percpu_devid_irq+0xdc/0x414
[ 3458.203385][ C5] handle_domain_irq+0xa8/0x168
[ 3458.208241][ C5] gic_handle_irq.34493+0x54/0x244
[ 3458.213359][ C5] call_on_irq_stack+0x40/0x70
[ 3458.218125][ C5] do_interrupt_handler+0x60/0x9c
[ 3458.223156][ C5] el1_interrupt+0x34/0x64
[ 3458.227560][ C5] el1h_64_irq_handler+0x1c/0x2c
[ 3458.232503][ C5] el1h_64_irq+0x7c/0x80
[ 3458.236736][ C5] free_vmap_area_noflush+0x108/0x39c
[ 3458.242126][ C5] remove_vm_area+0xbc/0x118
[ 3458.246714][ C5] vm_remove_mappings+0x48/0x2a4
[ 3458.251656][ C5] __vunmap+0x154/0x278
[ 3458.255796][ C5] stolen_time_cpu_down_prepare+0xc0/0xd8
[ 3458.261542][ C5] cpuhp_invoke_callback+0x248/0xc34
[ 3458.266842][ C5] cpuhp_thread_fun+0x1c4/0x248
[ 3458.271696][ C5] smpboot_thread_fn+0x1b0/0x400
[ 3458.276638][ C5] kthread+0x17c/0x1e0
[ 3458.280691][ C5] ret_from_fork+0x10/0x20

As a fix, introduce rcu lock to update stolen time structure.

Fixes: 75df529bec91 ("arm64: paravirt: Initialize steal time when cpu is online")
Cc: stable@vger.kernel.org
Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
Reviewed-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Link: https://lore.kernel.org/r/20220513174654.362169-1-quic_eberman@quicinc.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm64/kernel/paravirt.c | 29 +++++++++++++++++++++--------
1 file changed, 21 insertions(+), 8 deletions(-)

--- a/arch/arm64/kernel/paravirt.c
+++ b/arch/arm64/kernel/paravirt.c
@@ -35,7 +35,7 @@ static u64 native_steal_clock(int cpu)
DEFINE_STATIC_CALL(pv_steal_clock, native_steal_clock);

struct pv_time_stolen_time_region {
- struct pvclock_vcpu_stolen_time *kaddr;
+ struct pvclock_vcpu_stolen_time __rcu *kaddr;
};

static DEFINE_PER_CPU(struct pv_time_stolen_time_region, stolen_time_region);
@@ -52,7 +52,9 @@ early_param("no-steal-acc", parse_no_ste
/* return stolen time in ns by asking the hypervisor */
static u64 para_steal_clock(int cpu)
{
+ struct pvclock_vcpu_stolen_time *kaddr = NULL;
struct pv_time_stolen_time_region *reg;
+ u64 ret = 0;

reg = per_cpu_ptr(&stolen_time_region, cpu);

@@ -61,28 +63,37 @@ static u64 para_steal_clock(int cpu)
* online notification callback runs. Until the callback
* has run we just return zero.
*/
- if (!reg->kaddr)
+ rcu_read_lock();
+ kaddr = rcu_dereference(reg->kaddr);
+ if (!kaddr) {
+ rcu_read_unlock();
return 0;
+ }

- return le64_to_cpu(READ_ONCE(reg->kaddr->stolen_time));
+ ret = le64_to_cpu(READ_ONCE(kaddr->stolen_time));
+ rcu_read_unlock();
+ return ret;
}

static int stolen_time_cpu_down_prepare(unsigned int cpu)
{
+ struct pvclock_vcpu_stolen_time *kaddr = NULL;
struct pv_time_stolen_time_region *reg;

reg = this_cpu_ptr(&stolen_time_region);
if (!reg->kaddr)
return 0;

- memunmap(reg->kaddr);
- memset(reg, 0, sizeof(*reg));
+ kaddr = rcu_replace_pointer(reg->kaddr, NULL, true);
+ synchronize_rcu();
+ memunmap(kaddr);

return 0;
}

static int stolen_time_cpu_online(unsigned int cpu)
{
+ struct pvclock_vcpu_stolen_time *kaddr = NULL;
struct pv_time_stolen_time_region *reg;
struct arm_smccc_res res;

@@ -93,17 +104,19 @@ static int stolen_time_cpu_online(unsign
if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
return -EINVAL;

- reg->kaddr = memremap(res.a0,
+ kaddr = memremap(res.a0,
sizeof(struct pvclock_vcpu_stolen_time),
MEMREMAP_WB);

+ rcu_assign_pointer(reg->kaddr, kaddr);
+
if (!reg->kaddr) {
pr_warn("Failed to map stolen time data structure\n");
return -ENOMEM;
}

- if (le32_to_cpu(reg->kaddr->revision) != 0 ||
- le32_to_cpu(reg->kaddr->attributes) != 0) {
+ if (le32_to_cpu(kaddr->revision) != 0 ||
+ le32_to_cpu(kaddr->attributes) != 0) {
pr_warn_once("Unexpected revision or attributes in stolen time data\n");
return -ENXIO;
}