linux-kernel - [PATCH linux 3/8] x86/xen: use xen_vcpu_id mapping for HYPERVISOR_vcpu

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Date:	Tue, 28 Jun 2016 18:47:24 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	xen-devel@...ts.xenproject.org
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Stefano Stabellini <sstabellini@...nel.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Juergen Gross <jgross@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Julien Grall <julien.grall@...rix.com>
Subject: [PATCH linux 3/8] x86/xen: use xen_vcpu_id mapping for HYPERVISOR_vcpu_op

HYPERVISOR_vcpu_op passes Linux's idea of vCPU id as a parameter while
Xen's idea is expected. In some cases these ideas diverge so we need to
do remapping.

There is an issue, however. PV guests do VCPUOP_is_up very early
(see xen_fill_possible_map() and xen_filter_cpu_maps()) when we don't have
perpu areas initialized. While it could be solved with switching to
early_percpu for xen_vcpu_id I think it's not worth it: PV guests will
probably never get to the point where their idea of vCPU id diverges from
Xen's.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/include/asm/xen/hypercall.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h
index a12a047..20750c8 100644
--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -49,6 +49,7 @@
 #include <xen/interface/physdev.h>
 #include <xen/interface/platform.h>
 #include <xen/interface/xen-mca.h>
+#include <xen/xen-ops.h>
 
 /*
  * The hypercall asms have to meet several constraints:
@@ -422,7 +423,15 @@ HYPERVISOR_vm_assist(unsigned int cmd, unsigned int type)
 static inline int
 HYPERVISOR_vcpu_op(int cmd, int vcpuid, void *extra_args)
 {
-	return _hypercall3(int, vcpu_op, cmd, vcpuid, extra_args);
+	/*
+	 * PV guests call HYPERVISOR_vcpu_op before percpu areas are
+	 * initialized. As we always use direct mapping for vCPU ids
+	 * for them we can simply use Linux vcpuid here.
+	 */
+	return _hypercall3(int, vcpu_op, cmd,
+			   per_cpu(xen_vcpu_id, vcpuid) != -1 ?
+			   per_cpu(xen_vcpu_id, vcpuid) : vcpuid,
+			   extra_args);
 }
 
 #ifdef CONFIG_X86_64
-- 
2.5.5