[Xen-devel] [PATCH 4.14 124/156] x86/xen: Support early interrupts in xen pv guests

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Juergen Gross <jgross@xxxxxxxx>


[ Upstream commit 42b3a4cb5609de757f5445fcad18945ba9239a07 ]

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@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: boris.ostrovsky@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20171124084221.30172-1-jgross@xxxxxxxx
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/segment.h |   12 ++++++++++++
 arch/x86/mm/extable.c          |    4 +++-
 arch/x86/xen/enlighten_pv.c    |   37 ++++++++++++++++++++++++-------------
 arch/x86/xen/xen-asm_64.S      |   14 ++++++++++++++
 4 files changed, 53 insertions(+), 14 deletions(-)

--- 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.
--- 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
         * 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;
 
        /*
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -622,7 +622,7 @@ static struct trap_array_entry trap_arra
        { 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, u
                }
        }
 
+       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;
 
@@ -1261,6 +1269,21 @@ asmlinkage __visible void __init xen_sta
        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
@@ -1294,18 +1317,6 @@ asmlinkage __visible void __init xen_sta
         */
        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();
--- 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:



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