linux-kernel - [XEN PATCH 1/2] hvm: Support more than 32 VCPUS when migrating.

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Message-Id: <1396977950-8789-2-git-send-email-konrad@kernel.org>
Date:	Tue,  8 Apr 2014 13:25:49 -0400
From:	konrad@...nel.org
To:	xen-devel@...ts.xenproject.org, david.vrabel@...rix.com,
	boris.ostrovsky@...cle.com, linux-kernel@...r.kernel.org,
	keir@....org, jbeulich@...e.com
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: [XEN PATCH 1/2] hvm: Support more than 32 VCPUS when migrating.

From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

When we migrate an HVM guest, by default our shared_info can
only hold up to 32 CPUs. As such the hypercall
VCPUOP_register_vcpu_info was introduced which allowed us to
setup per-page areas for VCPUs. This means we can boot PVHVM
guest with more than 32 VCPUs. During migration the per-cpu
structure is allocated fresh by the hypervisor (vcpu_info_mfn
is set to INVALID_MFN) so that the newly migrated guest
can do make the VCPUOP_register_vcpu_info hypercall.

Unfortunatly we end up triggering this condition:
/* Run this command on yourself or on other offline VCPUS. */
 if ( (v != current) && !test_bit(_VPF_down, &v->pause_flags) )

which means we are unable to setup the per-cpu VCPU structures
for running vCPUS. The Linux PV code paths make this work by
iterating over every vCPU with:

 1) is target CPU up (VCPUOP_is_up hypercall?)
 2) if yes, then VCPUOP_down to pause it.
 3) VCPUOP_register_vcpu_info
 4) if it was down, then VCPUOP_up to bring it back up

But since VCPUOP_down, VCPUOP_is_up, and VCPUOP_up are
not allowed on HVM guests we can't do this. This patch
enables this.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
---
 xen/arch/x86/hvm/hvm.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 38c491e..b5b92fe 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3470,6 +3470,9 @@ static long hvm_vcpu_op(
     case VCPUOP_stop_singleshot_timer:
     case VCPUOP_register_vcpu_info:
     case VCPUOP_register_vcpu_time_memory_area:
+    case VCPUOP_down:
+    case VCPUOP_up:
+    case VCPUOP_is_up:
         rc = do_vcpu_op(cmd, vcpuid, arg);
         break;
     default:
-- 
1.7.7.6

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