Re: [PATCH] xen: vcpu_info reinit error after 'xl save -c' & 'xl restore' on PVOPS VM which has multi-cpu
From: Boris Ostrovsky
Date: Fri May 01 2015 - 14:57:35 EST
On 04/30/2015 03:27 AM, Ouyang Zhaowei (Charles) wrote:
On 2015.4.29 5:31, Boris Ostrovsky wrote:
On 04/28/2015 08:30 AM, Ouyang Zhaowei (Charles) wrote:
On 2015.4.26 7:31, Boris Ostrovsky wrote:
On 04/24/2015 05:30 AM, Ouyang Zhaowei (Charles) wrote:
If a PVOPS VM has multi-cpu the vcpu_info of cpu0 is the member of the structure HYPERVISOR_shared_info,
and the others is not, but after 'xl save -c/restore' the vcpu_info will be reinitialized,
the vcpu_info of all the vcpus will be considered as the member of HYPERVISOR_shared_info.
This will cause the cpu1 and other cpu keep receiving interrupts, and the cpu0 is waiting them to
finish the job.
So we do not reinit the vcpu_info when PVOPS vm is doing 'xl save -c/restore'.
Signed-off-by: Charles Ouyang <ouyangzhaowei@xxxxxxxxxx>
---
arch/x86/xen/suspend.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
index d949769..b2bed45 100644
--- a/arch/x86/xen/suspend.c
+++ b/arch/x86/xen/suspend.c
@@ -32,7 +32,8 @@ static void xen_hvm_post_suspend(int suspend_cancelled)
{
#ifdef CONFIG_XEN_PVHVM
int cpu;
- xen_hvm_init_shared_info();
+ if (!suspend_cancelled)
+ xen_hvm_init_shared_info();
xen_callback_vector();
xen_unplug_emulated_devices();
if (xen_feature(XENFEAT_hvm_safe_pvclock)) {
Do we need to call other routines if suspend is canceled?
Also, if suspend is canceled then we don't do xen_irq_resume() if that's what you meant by "vcpu_info will be reinitialized". Were you referring some other re-initialization?
Hi Boris,
Sorry I didn't make myself clear.
About the "vcpu_info reinitialize", I mean in the function "xen_hvm_init_shared_info()" the pointer "xen_vcpu" will be reset and all
point to HYPERVISOR_shared_info->vcpu_info[cpu].
void __ref xen_hvm_init_shared_info(void)
----
1702 * When xen_hvm_init_shared_info is run at boot time only vcpu 0 is
1703 * online but xen_hvm_init_shared_info is run at resume time too and
1704 * in that case multiple vcpus might be online. */
1705 for_each_online_cpu(cpu) {
1706 /* Leave it to be NULL. */
1707 if (cpu >= MAX_VIRT_CPUS)
1708 continue;
1709 per_cpu(xen_vcpu, cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];
1710 }
1711 }
But on Xen boot the init function "xen_start_kernel" only set the cpu0 to point to HYPERVISOR_shared_info->vcpu_info[0]
asmlinkage __visible void __init xen_start_kernel(void)
We are talking about HVM guests here and xen_start_kernel is only called for PV. But even if it was, xen_vcpu pointers for other VCPUs are set in xen_vcpu_setup(), which is called when non-boot VCPUs are coming up.
And I wonder whether the actual problem is that we don't call xen_vcpu_setup() on canceled suspend (as we don't need to, really) and therefore if we call xen_hvm_init_shared_info() then per_cpu(xen_vcpu,cpu) for *non-boot* cpus is will become wrong.
Yes, you are right, in xen_vcpu_setup() non-boot VCPUs is set to point to xen_vcpu_info
static void xen_vcpu_setup(int cpu)
----
208 vcpup = &per_cpu(xen_vcpu_info, cpu);
...
227 /* This cpu is using the registered vcpu info, even if
228 later ones fail to. */
229 per_cpu(xen_vcpu, cpu) = vcpup;
But on canceled suspend if we call xen_hvm_init_shared_info(), the non-boot VCPUS will be reset to point to HYPERVISOR_shared_info->vcpu_info[cpu] which is a wrong address.
So I suggest we don't call xen_hvm_init_shared_info() when suspend is canceled.
Right, so can you resubmit the patch with updated commit message? (Just
note there that the hypervisor continues assuming that vcpu_info is
stored in per-cpu data which was set up by xen_vcpu_setup(), while the
call to xen_hvm_init_shared_info() will now make the guest think that
vcpu_info is in the shared page).
Thanks.
-boris
-boris
----
1563 /* Don't do the full vcpu_info placement stuff until we have a
1564 possible map and a non-dummy shared_info. */
1565 per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];
1566
1567 local_irq_disable();
Other cpus are set to point to "xen_vcpu_info" in function xen_vcpu_setup().
So after xl save -c/restore, the pointer xen_vcpu will be reset in function "xen_hvm_init_shared_info" and point to a wrong place.
This may cause all the cpus cannot handle irqs except cpu0, so IMHO it's not necessary to call xen_hvm_init_shared_info again if
suspend is canceled.
(The patch itself looks like the right thing to do though).
-boris
.
.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/