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[Xen-devel] __HYPERVISOR_COMPAT_VIRT_START for HVM guest with PV drivers



Do the guest virtual addresses passed by a hypervisor call on a 32-bit HVM with PV drivers guest to a 64-bit hypervisor need to lie below __HYPERVISOR_COMPAT_VIRT_START? Both HVM and PVM domains have their hv_compat_vstart set to __HYPERVISOR_COMPAT_VIRT_START. The hypervisor's compat layer is causing the balloon driver's HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation) hypervisor call to error out in xen/common/compat/memory.c compat_memory_op(), compat_handle_ok(), because the PVHVM guest's extent_start lies above __HYPERVISOR_COMPAT_VIRT_START. The following patch appears to fix the problem but I want to make sure it is fixing the real bug:

diff -up xen-3.4.0/xen/arch/x86/domain.c.orig xen-3.4.0/xen/arch/x86/domain.c --- xen-3.4.0/xen/arch/x86/domain.c.orig 2009-08-18 13:09:30.000000000 -0700
+++ xen-3.4.0/xen/arch/x86/domain.c     2009-08-18 14:55:08.000000000 -0700
@@ -428,7 +428,12 @@ int arch_domain_create(struct domain *d,
#endif /* __x86_64__ */

#ifdef CONFIG_COMPAT
-    HYPERVISOR_COMPAT_VIRT_START(d) = __HYPERVISOR_COMPAT_VIRT_START;
+    if (is_hvm_domain(d)) {
+ HYPERVISOR_COMPAT_VIRT_START(d) = __HYPERVISOR_COMPAT_VIRT_START_NONE;
+    }
+    else {
+        HYPERVISOR_COMPAT_VIRT_START(d) = __HYPERVISOR_COMPAT_VIRT_START;
+    }
#endif

   if ( (rc = paging_domain_init(d)) != 0 )
diff -up xen-3.4.0/xen/include/asm-x86/config.h.orig xen-3.4.0/xen/include/asm-x86/config.h --- xen-3.4.0/xen/include/asm-x86/config.h.orig 2009-08-18 13:22:16.000000000 -0700 +++ xen-3.4.0/xen/include/asm-x86/config.h 2009-08-18 14:54:40.000000000 -0700
@@ -228,6 +228,7 @@ extern unsigned int video_mode, video_fl

#ifndef __ASSEMBLY__

+#define __HYPERVISOR_COMPAT_VIRT_START_NONE 0xFFFFFFFF
/* This is not a fixed value, just a lower limit. */
#define __HYPERVISOR_COMPAT_VIRT_START 0xF5800000
#define HYPERVISOR_COMPAT_VIRT_START(d) ((d)->arch.hv_compat_vstart)

Thanks,
Chuck

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