x86/xen: Support early interrupts in xen pv guests

Add early interrupt handlers activated by idt_setup_early_handler() to
the handlers supported by Xen pv guests. This will allow for early
WARN() calls not crashing the guest.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel@lists.xenproject.org
Cc: boris.ostrovsky@oracle.com
Link: https://lkml.kernel.org/r/20171124084221.30172-1-jgross@suse.com

4 files changed, 53 insertions, 14 deletions

diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
index b20f9d623f9c..8f09012b92e7 100644
--- a/arch/x86/include/asm/segment.h
+++ b/arch/x86/include/asm/segment.h
@@ -236,11 +236,23 @@
  */
 #define EARLY_IDT_HANDLER_SIZE 9
 
+/*
+ * xen_early_idt_handler_array is for Xen pv guests: for each entry in
+ * early_idt_handler_array it contains a prequel in the form of
+ * pop %rcx; pop %r11; jmp early_idt_handler_array[i]; summing up to
+ * max 8 bytes.
+ */
+#define XEN_EARLY_IDT_HANDLER_SIZE 8
+
 #ifndef __ASSEMBLY__
 
 extern const char early_idt_handler_array[NUM_EXCEPTION_VECTORS][EARLY_IDT_HANDLER_SIZE];
 extern void early_ignore_irq(void);
 
+#if defined(CONFIG_X86_64) && defined(CONFIG_XEN_PV)
+extern const char xen_early_idt_handler_array[NUM_EXCEPTION_VECTORS][XEN_EARLY_IDT_HANDLER_SIZE];
+#endif
+
 /*
  * Load a segment. Fall back on loading the zero segment if something goes
  * wrong.  This variant assumes that loading zero fully clears the segment.
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 3321b446b66c..88754bfd425f 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -1,6 +1,7 @@
 #include <linux/extable.h>
 #include <linux/uaccess.h>
 #include <linux/sched/debug.h>
+#include <xen/xen.h>
 
 #include <asm/fpu/internal.h>
 #include <asm/traps.h>
@@ -212,8 +213,9 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
          * Old CPUs leave the high bits of CS on the stack
          * undefined.  I'm not sure which CPUs do this, but at least
          * the 486 DX works this way.
+         * Xen pv domains are not using the default __KERNEL_CS.
          */
-        if (regs->cs != __KERNEL_CS)
+        if (!xen_pv_domain() && regs->cs != __KERNEL_CS)
                 goto fail;
 
         /*
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 5b2b3f3f6531..f2414c6c5e7c 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -622,7 +622,7 @@ static struct trap_array_entry trap_array[] = {
         { simd_coprocessor_error,      xen_simd_coprocessor_error,      false },
 };
 
-static bool get_trap_addr(void **addr, unsigned int ist)
+static bool __ref get_trap_addr(void **addr, unsigned int ist)
 {
         unsigned int nr;
         bool ist_okay = false;
@@ -644,6 +644,14 @@ static bool get_trap_addr(void **addr, unsigned int ist)
                 }
         }
 
+        if (nr == ARRAY_SIZE(trap_array) &&
+            *addr >= (void *)early_idt_handler_array[0] &&
+            *addr < (void *)early_idt_handler_array[NUM_EXCEPTION_VECTORS]) {
+                nr = (*addr - (void *)early_idt_handler_array[0]) /
+                     EARLY_IDT_HANDLER_SIZE;
+                *addr = (void *)xen_early_idt_handler_array[nr];
+        }
+
         if (WARN_ON(ist != 0 && !ist_okay))
                 return false;
 
@@ -1262,6 +1270,21 @@ asmlinkage __visible void __init xen_start_kernel(void)
         xen_setup_gdt(0);
 
         xen_init_irq_ops();
+
+        /* Let's presume PV guests always boot on vCPU with id 0. */
+        per_cpu(xen_vcpu_id, 0) = 0;
+
+        /*
+         * Setup xen_vcpu early because idt_setup_early_handler needs it for
+         * local_irq_disable(), irqs_disabled().
+         *
+         * Don't do the full vcpu_info placement stuff until we have
+         * the cpu_possible_mask and a non-dummy shared_info.
+         */
+        xen_vcpu_info_reset(0);
+
+        idt_setup_early_handler();
+
         xen_init_capabilities();
 
 #ifdef CONFIG_X86_LOCAL_APIC
@@ -1295,18 +1318,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
          */
         acpi_numa = -1;
 #endif
-        /* Let's presume PV guests always boot on vCPU with id 0. */
-        per_cpu(xen_vcpu_id, 0) = 0;
-
-        /*
-         * Setup xen_vcpu early because start_kernel needs it for
-         * local_irq_disable(), irqs_disabled().
-         *
-         * Don't do the full vcpu_info placement stuff until we have
-         * the cpu_possible_mask and a non-dummy shared_info.
-         */
-        xen_vcpu_info_reset(0);
-
         WARN_ON(xen_cpuhp_setup(xen_cpu_up_prepare_pv, xen_cpu_dead_pv));
 
         local_irq_disable();
diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index 8a10c9a9e2b5..417b339e5c8e 100644
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -15,6 +15,7 @@
 
 #include <xen/interface/xen.h>
 
+#include <linux/init.h>
 #include <linux/linkage.h>
 
 .macro xen_pv_trap name
@@ -54,6 +55,19 @@ xen_pv_trap entry_INT80_compat
 #endif
 xen_pv_trap hypervisor_callback
 
+        __INIT
+ENTRY(xen_early_idt_handler_array)
+        i = 0
+        .rept NUM_EXCEPTION_VECTORS
+        pop %rcx
+        pop %r11
+        jmp early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE
+        i = i + 1
+        .fill xen_early_idt_handler_array + i*XEN_EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc
+        .endr
+END(xen_early_idt_handler_array)
+        __FINIT
+
 hypercall_iret = hypercall_page + __HYPERVISOR_iret * 32
 /*
  * Xen64 iret frame: