xen/pvh*: Support > 32 VCPUs at domain restore

When Xen restores a PVHVM or PVH guest, its shared_info only holds
up to 32 CPUs. The hypercall VCPUOP_register_vcpu_info allows
us to setup per-page areas for VCPUs. This means we can boot
PVH* guests with more than 32 VCPUs. During restore the per-cpu
structure is allocated freshly by the hypervisor (vcpu_info_mfn is
set to INVALID_MFN) so that the newly restored guest can make a
VCPUOP_register_vcpu_info hypercall.

However, we end up triggering this condition in Xen:
/* 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 makes this work by
iterating over cpu_possible in xen_vcpu_restore() 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

With Xen commit 192df6f9122d ("xen/x86: allow HVM guests to use
hypercalls to bring up vCPUs") this is available for non-PV guests.
As such first check if VCPUOP_is_up is actually possible before
trying this dance.

As most of this dance code is done already in xen_vcpu_restore()
let's make it callable on PV, PVH and PVHVM.

Based-on-patch-by: Konrad Wilk <konrad.wilk@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

1 files changed, 7 insertions, 13 deletions

diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index eb53da6547ee..ba1afadb2512 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -20,7 +20,6 @@
 
 void __ref xen_hvm_init_shared_info(void)
 {
-	int cpu;
 	struct xen_add_to_physmap xatp;
 	static struct shared_info *shared_info_page;
 
@@ -35,18 +34,6 @@ void __ref xen_hvm_init_shared_info(void)
 		BUG();
 
 	HYPERVISOR_shared_info = (struct shared_info *)shared_info_page;
-
-	/* xen_vcpu is a pointer to the vcpu_info struct in the shared_info
-	 * page, we use it in the event channel upcall and in some pvclock
-	 * related functions. We don't need the vcpu_info placement
-	 * optimizations because we don't use any pv_mmu or pv_irq op on
-	 * HVM.
-	 * When xen_hvm_init_shared_info is run at boot time only vcpu 0 is
-	 * online but xen_hvm_init_shared_info is run at resume time too and
-	 * in that case multiple vcpus might be online. */
-	for_each_online_cpu(cpu) {
-		xen_vcpu_info_reset(cpu);
-	}
 }
 
 static void __init init_hvm_pv_info(void)
@@ -150,6 +137,13 @@ static void __init xen_hvm_guest_init(void)
 
 	xen_hvm_init_shared_info();
 
+	/*
+	 * xen_vcpu is a pointer to the vcpu_info struct in the shared_info
+	 * page, we use it in the event channel upcall and in some pvclock
+	 * related functions.
+	 */
+	xen_vcpu_info_reset(0);
+
 	xen_panic_handler_init();
 
 	if (xen_feature(XENFEAT_hvm_callback_vector))