hypervisor/x86/xen: Unset X86_BUG_SYSRET_SS_ATTRS on Xen PV guests

Commit 61f01dd941ba ("x86_64, asm: Work around AMD SYSRET SS descriptor
attribute issue") makes AMD processors set SS to __KERNEL_DS in
__switch_to() to deal with cases when SS is NULL.

This breaks Xen PV guests who do not want to load SS with__KERNEL_DS.

Since the problem that the commit is trying to address would have to be
fixed in the hypervisor (if it in fact exists under Xen) there is no
reason to set X86_BUG_SYSRET_SS_ATTRS flag for PV VPCUs here.

This can be easily achieved by adding x86_hyper_xen_hvm.set_cpu_features
op which will clear this flag. (And since this structure is no longer
HVM-specific we should do some renaming).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

diff --git a/arch/x86/include/asm/hypervisor.h b/arch/x86/include/asm/hypervisor.h
index e42f758a0fbd9b14b38feaae9fbb3f1a2bfcd204..055ea9941dd5f671d116306a6544adf7a4f189bc 100644 (file)
--- a/arch/x86/include/asm/hypervisor.h
+++ b/arch/x86/include/asm/hypervisor.h
@@ -50,7 +50,7 @@ extern const struct hypervisor_x86 *x86_hyper;
 /* Recognized hypervisors */
 extern const struct hypervisor_x86 x86_hyper_vmware;
 extern const struct hypervisor_x86 x86_hyper_ms_hyperv;
-extern const struct hypervisor_x86 x86_hyper_xen_hvm;
+extern const struct hypervisor_x86 x86_hyper_xen;
 extern const struct hypervisor_x86 x86_hyper_kvm;
 
 extern void init_hypervisor(struct cpuinfo_x86 *c);

diff --git a/arch/x86/kernel/cpu/hypervisor.c b/arch/x86/kernel/cpu/hypervisor.c
index 36ce402a3fa5b311014b30e3dd8cac69d5f68a88..d820d8eae96be0b3daa0ec01d9f4a22bf1ad930e 100644 (file)
--- a/arch/x86/kernel/cpu/hypervisor.c
+++ b/arch/x86/kernel/cpu/hypervisor.c
@@ -27,8 +27,8 @@
 
 static const __initconst struct hypervisor_x86 * const hypervisors[] =
 {
-#ifdef CONFIG_XEN_PVHVM
-       &x86_hyper_xen_hvm,
+#ifdef CONFIG_XEN
+       &x86_hyper_xen,
 #endif
        &x86_hyper_vmware,
        &x86_hyper_ms_hyperv,

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 94578efd3067f0a0fd86c36c5b3be07eced3d509..46957ead3060eecb5e76b6f6daf3b498a6b6a5e9 100644 (file)
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1760,6 +1760,9 @@ static struct notifier_block xen_hvm_cpu_notifier = {
 
 static void __init xen_hvm_guest_init(void)
 {
+       if (xen_pv_domain())
+               return;
+
        init_hvm_pv_info();
 
        xen_hvm_init_shared_info();
@@ -1775,6 +1778,7 @@ static void __init xen_hvm_guest_init(void)
        xen_hvm_init_time_ops();
        xen_hvm_init_mmu_ops();
 }
+#endif
 
 static bool xen_nopv = false;
 static __init int xen_parse_nopv(char *arg)
@@ -1784,14 +1788,11 @@ static __init int xen_parse_nopv(char *arg)
 }
 early_param("xen_nopv", xen_parse_nopv);
 
-static uint32_t __init xen_hvm_platform(void)
+static uint32_t __init xen_platform(void)
 {
        if (xen_nopv)
                return 0;
 
-       if (xen_pv_domain())
-               return 0;
-
        return xen_cpuid_base();
 }
 
@@ -1809,11 +1810,19 @@ bool xen_hvm_need_lapic(void)
 }
 EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
 
-const struct hypervisor_x86 x86_hyper_xen_hvm __refconst = {
-       .name                   = "Xen HVM",
-       .detect                 = xen_hvm_platform,
+static void xen_set_cpu_features(struct cpuinfo_x86 *c)
+{
+       if (xen_pv_domain())
+               clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+}
+
+const struct hypervisor_x86 x86_hyper_xen = {
+       .name                   = "Xen",
+       .detect                 = xen_platform,
+#ifdef CONFIG_XEN_PVHVM
        .init_platform          = xen_hvm_guest_init,
+#endif
        .x2apic_available       = xen_x2apic_para_available,
+       .set_cpu_features       = xen_set_cpu_features,
 };
-EXPORT_SYMBOL(x86_hyper_xen_hvm);
-#endif
+EXPORT_SYMBOL(x86_hyper_xen);