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Subject[tip:x86/urgent] x86/xen: Support early interrupts in xen pv guests
Commit-ID:  42b3a4cb5609de757f5445fcad18945ba9239a07
Gitweb: https://git.kernel.org/tip/42b3a4cb5609de757f5445fcad18945ba9239a07
Author: Juergen Gross <jgross@suse.com>
AuthorDate: Fri, 24 Nov 2017 09:42:21 +0100
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 28 Nov 2017 00:28:56 +0100

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

---
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(-)

diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
index b20f9d6..8f09012b 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 3321b44..88754bf 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 5b2b3f3..f2414c6 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 8a10c9a..417b339 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:
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