[Xen-devel] [V2 PATCH 1/1] PVH: set EFER.NX and EFER.SCE

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

This patch addresses two things for a pvh boot vcpu:

  - NX bug on intel: It was recenlty discovered that NX is not being
    honored in PVH on intel since EFER.NX is not being set.

  - PVH boot hang on newer xen:  Following c/s on xen

        c/s 7645640:  x86/PVH: don't set EFER_SCE for pvh guest

    removes setting of EFER.SCE for PVH guests. As such, existing intel
    pvh guest will no longer boot on xen after that c/s.

Both above changes will be applicable to AMD also when xen support
of AMD pvh is added.

Also, we create a new glue assembly entry point for secondary vcpus
because they come up on kernel page tables that have pte.NX
bits set. As such, before anything is touched in DS/SS, EFER.NX
must be set.

Signed-off-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
---
 arch/x86/xen/enlighten.c |  3 +++
 arch/x86/xen/smp.c       | 28 ++++++++++++++++++++--------
 arch/x86/xen/smp.h       |  1 +
 arch/x86/xen/xen-head.S  | 29 +++++++++++++++++++++++++++++
 4 files changed, 53 insertions(+), 8 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c0cb11f..e17fa2d 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -85,6 +85,8 @@
 
 EXPORT_SYMBOL_GPL(hypercall_page);
 
+extern void xen_pvh_configure_efer(void);
+
 /*
  * Pointer to the xen_vcpu_info structure or
  * &HYPERVISOR_shared_info->vcpu_info[cpu]. See xen_hvm_init_shared_info
@@ -1508,6 +1510,7 @@ static void __init xen_pvh_early_guest_init(void)
                return;
 
        xen_have_vector_callback = 1;
+       xen_pvh_configure_efer();
        xen_pvh_set_cr_flags(0);
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 7005974..073bbf4 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -37,6 +37,7 @@
 #include <xen/hvc-console.h>
 #include "xen-ops.h"
 #include "mmu.h"
+#include "smp.h"
 
 cpumask_var_t xen_cpu_initialized_map;
 
@@ -99,8 +100,12 @@ static void cpu_bringup(void)
        wmb();                  /* make sure everything is out */
 }
 
-/* Note: cpu parameter is only relevant for PVH */
-static void cpu_bringup_and_idle(int cpu)
+/*
+ * Note: cpu parameter is only relevant for PVH. The reason for passing it
+ * is we can't do smp_processor_id until the percpu segments are loaded, for
+ * which we need the cpu number! So we pass it in rdi as first parameter.
+ */
+asmlinkage __visible void cpu_bringup_and_idle(int cpu)
 {
 #ifdef CONFIG_X86_64
        if (xen_feature(XENFEAT_auto_translated_physmap) &&
@@ -374,11 +379,10 @@ cpu_initialize_context(unsigned int cpu, struct 
task_struct *idle)
        ctxt->user_regs.fs = __KERNEL_PERCPU;
        ctxt->user_regs.gs = __KERNEL_STACK_CANARY;
 #endif
-       ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;
-
        memset(&ctxt->fpu_ctxt, 0, sizeof(ctxt->fpu_ctxt));
 
        if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+               ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;
                ctxt->flags = VGCF_IN_KERNEL;
                ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */
                ctxt->user_regs.ds = __USER_DS;
@@ -416,12 +420,20 @@ cpu_initialize_context(unsigned int cpu, struct 
task_struct *idle)
 #ifdef CONFIG_X86_32
        }
 #else
-       } else
-               /* N.B. The user_regs.eip (cpu_bringup_and_idle) is called with
-                * %rdi having the cpu number - which means are passing in
-                * as the first parameter the cpu. Subtle!
+       } else {
+               /*
+                * The vcpu comes on kernel page tables which have the NX pte
+                * bit set. This means before DS/SS is touched, NX in
+                * EFER must be set. Hence the following assembly glue code.
+                */
+               ctxt->user_regs.eip = (unsigned long)pvh_smp_cpu_bringup;
+
+               /* N.B. The bringup function cpu_bringup_and_idle is called with
+                * %rdi having the cpu number - which means we are passing it in
+                * as the first parameter. Subtle!
                 */
                ctxt->user_regs.rdi = cpu;
+       }
 #endif
        ctxt->user_regs.esp = idle->thread.sp0 - sizeof(struct pt_regs);
        ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_mfn(swapper_pg_dir));
diff --git a/arch/x86/xen/smp.h b/arch/x86/xen/smp.h
index c7c2d89..d6628cb 100644
--- a/arch/x86/xen/smp.h
+++ b/arch/x86/xen/smp.h
@@ -7,5 +7,6 @@ extern void xen_send_IPI_mask_allbutself(const struct cpumask 
*mask,
 extern void xen_send_IPI_allbutself(int vector);
 extern void xen_send_IPI_all(int vector);
 extern void xen_send_IPI_self(int vector);
+extern void pvh_smp_cpu_bringup(int cpu);
 
 #endif
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 485b695..97ee831 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -47,6 +47,35 @@ ENTRY(startup_xen)
 
        __FINIT
 
+#ifdef CONFIG_XEN_PVH
+#ifdef CONFIG_X86_64
+.macro PVH_EARLY_SET_EFER
+       /* Gather features to see if NX implemented. */
+       movl    $0x80000001, %eax
+       cpuid
+       movl    %edx,%esi
+
+       movl    $MSR_EFER, %ecx
+       rdmsr
+       btsl    $_EFER_SCE, %eax
+
+       btl     $20,%esi
+       jnc     1f      /* No NX, skip setting it */
+       btsl    $_EFER_NX, %eax
+1:     wrmsr
+.endm
+
+ENTRY(xen_pvh_configure_efer)
+       PVH_EARLY_SET_EFER
+       ret
+
+/* Note that rdi contains the cpu number and must be preserved */
+ENTRY(pvh_smp_cpu_bringup)
+       PVH_EARLY_SET_EFER
+       jmp cpu_bringup_and_idle
+#endif /* CONFIG_X86_64 */
+#endif /* CONFIG_XEN_PVH */
+
 .pushsection .text
        .balign PAGE_SIZE
 ENTRY(hypercall_page)
-- 
1.8.3.1


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