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Subject: Re: [V0 PATCH] xen/pvh: set some cr flags upon vcpu start
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Fri, 17 Jan 2014 22:56:24 -0500
To: Mukesh Rathor <mukesh.rathor@oracle.com>
CC: roger.pau@citrix.com, Xen-devel@lists.xensource.com,
        linux-kernel@vger.kernel.org
Message-ID: <11d39cdc-d0a7-4658-9ed5-f9fa1ca50aa1@email.android.com>
Sender: linux-kernel-owner@vger.kernel.org

Mukesh Rathor <mukesh.rathor@oracle.com> wrote:
>pvh was designed to start with pv flags, but a commit in xen tree
>51e2cac257ec8b4080d89f0855c498cbbd76a5e5 removed some of the flags as
>they are not necessary. As a result, these CR flags must be set in the
>guest.
>
>Signed-off-by: Roger Pau Monne <roger.pau@citrix.com>
>Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>
>---
>arch/x86/xen/enlighten.c |   43
>+++++++++++++++++++++++++++++++++++++------
> arch/x86/xen/smp.c       |    2 +-
> arch/x86/xen/xen-ops.h   |    2 +-
> 3 files changed, 39 insertions(+), 8 deletions(-)
>
>diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
>index 628099a..4a2aaa6 100644
>--- a/arch/x86/xen/enlighten.c
>+++ b/arch/x86/xen/enlighten.c
>@@ -1410,12 +1410,8 @@ static void __init
>xen_boot_params_init_edd(void)
>  * Set up the GDT and segment registers for -fstack-protector.  Until
>  * we do this, we have to be careful not to call any stack-protected
>  * function, which is most of the kernel.
>- *
>- * Note, that it is refok - because the only caller of this after init
>- * is PVH which is not going to use xen_load_gdt_boot or other
>- * __init functions.
>  */
>-void __ref xen_setup_gdt(int cpu)
>+static void xen_setup_gdt(int cpu)
> {
> 	if (xen_feature(XENFEAT_auto_translated_physmap)) {
> #ifdef CONFIG_X86_64
>@@ -1463,13 +1459,48 @@ void __ref xen_setup_gdt(int cpu)
> 	pv_cpu_ops.load_gdt = xen_load_gdt;
> }
> 
>+/*
>+ * A pv guest starts with default flags that are not set for pvh, set
>them
>+ * here asap.
>+ */
>+static void xen_pvh_set_cr_flags(int cpu)
>+{
>+	write_cr0(read_cr0() | X86_CR0_MP | X86_CR0_WP | X86_CR0_AM);

I think it would be good to mention that Xen unconditionally sets PE and ET for HVM guests and that additionally for PVH the PG is set.

What about the NE? That looks to be missing from the list above? Should we set it?

>+
>+	if (!cpu)
>+		return;
>+	/*
>+	 * Unlike PV, for pvh xen does not set: PSE PGE OSFXSR OSXMMEXCPT
>+	 * For BSP, PSE PGE will be set in probe_page_size_mask(), for AP
>+	 * set them here. For all, OSFXSR OSXMMEXCPT will be set in fpu_init
>+	 */
>+	if (cpu_has_pse)
>+		set_in_cr4(X86_CR4_PSE);
>+
>+	if (cpu_has_pge)
>+		set_in_cr4(X86_CR4_PGE);
>+}
>+
>+/*
>+ * Note, that it is refok - because the only caller of this after init
>+ * is PVH which is not going to use xen_load_gdt_boot or other
>+ * __init functions.
>+ */
>+void __ref xen_pvh_secondary_vcpu_init(int cpu)
>+{
>+	xen_setup_gdt(cpu);
>+	xen_pvh_set_cr_flags(cpu);
>+}
>+
> static void __init xen_pvh_early_guest_init(void)
> {
> 	if (!xen_feature(XENFEAT_auto_translated_physmap))
> 		return;
> 
>-	if (xen_feature(XENFEAT_hvm_callback_vector))
>+	if (xen_feature(XENFEAT_hvm_callback_vector)) {
> 		xen_have_vector_callback = 1;
>+		xen_pvh_set_cr_flags(0);
>+	}
> 
> #ifdef CONFIG_X86_32
> 	BUG(); /* PVH: Implement proper support. */
>diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
>index 5e46190..a18eadd 100644
>--- a/arch/x86/xen/smp.c
>+++ b/arch/x86/xen/smp.c
>@@ -105,7 +105,7 @@ static void cpu_bringup_and_idle(int cpu)
> #ifdef CONFIG_X86_64
> 	if (xen_feature(XENFEAT_auto_translated_physmap) &&
> 	    xen_feature(XENFEAT_supervisor_mode_kernel))
>-		xen_setup_gdt(cpu);
>+		xen_pvh_secondary_vcpu_init(cpu);
> #endif
> 	cpu_bringup();
> 	cpu_startup_entry(CPUHP_ONLINE);
>diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
>index 9059c24..1cb6f4c 100644
>--- a/arch/x86/xen/xen-ops.h
>+++ b/arch/x86/xen/xen-ops.h
>@@ -123,5 +123,5 @@ __visible void xen_adjust_exception_frame(void);
> 
> extern int xen_panic_handler_init(void);
> 
>-void xen_setup_gdt(int cpu);
>+void xen_pvh_secondary_vcpu_init(int cpu);
> #endif /* XEN_OPS_H */


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