[tip: x86/entry] x86/entry: Switch XEN/PV hypercall entry to IDTENTRY

From: tip-bot2 for Thomas Gleixner
Date: Wed May 27 2020 - 04:13:22 EST

The following commit has been merged into the x86/entry branch of tip:

Commit-ID: 66a07b44e7658da3145bb3a8f45256d103e3addc
Gitweb: https://git.kernel.org/tip/66a07b44e7658da3145bb3a8f45256d103e3addc
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Thu, 21 May 2020 22:05:26 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 26 May 2020 19:06:28 +02:00

x86/entry: Switch XEN/PV hypercall entry to IDTENTRY

Convert the XEN/PV hypercall to IDTENTRY:

- Emit the ASM stub with DECLARE_IDTENTRY
- Remove the ASM idtentry in 64-bit
- Remove the open coded ASM entry code in 32-bit
- Remove the old prototypes

The handler stubs need to stay in ASM code as they need corner case handling
and adjustment of the stack pointer.

Provide a new C function which invokes the entry/exit handling and calls
into the XEN handler on the interrupt stack if required.

The exit code is slightly different from the regular idtentry_exit() on
non-preemptible kernels. If the hypercall is preemptible and need_resched()
is set then XEN provides a preempt hypercall scheduling function.

Move this functionality into the entry code so it can use the existing
idtentry functionality.

[ mingo: Build fixes. ]

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>
Acked-by: Juergen Gross <jgross@xxxxxxxx>
Tested-by: Juergen Gross <jgross@xxxxxxxx>
Link: https://lore.kernel.org/r/20200521202118.055270078@xxxxxxxxxxxxx
---
arch/x86/entry/common.c | 74 ++++++++++++++++++++++++++++++++-
arch/x86/entry/entry_32.S | 17 +++----
arch/x86/entry/entry_64.S | 20 ++-------
arch/x86/include/asm/idtentry.h | 13 ++++++-
arch/x86/xen/setup.c | 4 +-
arch/x86/xen/smp_pv.c | 3 +-
arch/x86/xen/xen-asm_32.S | 12 ++---
arch/x86/xen/xen-asm_64.S | 2 +-
arch/x86/xen/xen-ops.h | 1 +-
drivers/xen/Makefile | 2 +-
drivers/xen/preempt.c | 42 +------------------
include/xen/xen-ops.h | 19 ++------
12 files changed, 123 insertions(+), 86 deletions(-)
delete mode 100644 drivers/xen/preempt.c

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 066215a..bb66f4d 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -27,6 +27,11 @@
#include <linux/syscalls.h>
#include <linux/uaccess.h>

+#ifdef CONFIG_XEN_PV
+#include <xen/xen-ops.h>
+#include <xen/events.h>
+#endif
+
#include <asm/desc.h>
#include <asm/traps.h>
#include <asm/vdso.h>
@@ -35,6 +40,7 @@
#include <asm/nospec-branch.h>
#include <asm/io_bitmap.h>
#include <asm/syscall.h>
+#include <asm/irq_stack.h>

#define CREATE_TRACE_POINTS
#include <trace/events/syscalls.h>
@@ -680,3 +686,71 @@ void noinstr idtentry_exit_user(struct pt_regs *regs)

prepare_exit_to_usermode(regs);
}
+
+#ifdef CONFIG_XEN_PV
+#ifndef CONFIG_PREEMPTION
+/*
+ * Some hypercalls issued by the toolstack can take many 10s of
+ * seconds. Allow tasks running hypercalls via the privcmd driver to
+ * be voluntarily preempted even if full kernel preemption is
+ * disabled.
+ *
+ * Such preemptible hypercalls are bracketed by
+ * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
+ * calls.
+ */
+DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
+EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
+
+/*
+ * In case of scheduling the flag must be cleared and restored after
+ * returning from schedule as the task might move to a different CPU.
+ */
+static __always_inline bool get_and_clear_inhcall(void)
+{
+ bool inhcall = __this_cpu_read(xen_in_preemptible_hcall);
+
+ __this_cpu_write(xen_in_preemptible_hcall, false);
+ return inhcall;
+}
+
+static __always_inline void restore_inhcall(bool inhcall)
+{
+ __this_cpu_write(xen_in_preemptible_hcall, inhcall);
+}
+#else
+static __always_inline bool get_and_clear_inhcall(void) { return false; }
+static __always_inline void restore_inhcall(bool inhcall) { }
+#endif
+
+static void __xen_pv_evtchn_do_upcall(void)
+{
+ irq_enter_rcu();
+ inc_irq_stat(irq_hv_callback_count);
+
+ xen_hvm_evtchn_do_upcall();
+
+ irq_exit_rcu();
+}
+
+__visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
+{
+ struct pt_regs *old_regs;
+ bool inhcall, rcu_exit;
+
+ rcu_exit = idtentry_enter_cond_rcu(regs);
+ old_regs = set_irq_regs(regs);
+
+ run_on_irqstack_cond(__xen_pv_evtchn_do_upcall, NULL, regs);
+
+ set_irq_regs(old_regs);
+
+ inhcall = get_and_clear_inhcall();
+ if (inhcall && !WARN_ON_ONCE(rcu_exit)) {
+ idtentry_exit_cond_resched(regs, true);
+ restore_inhcall(inhcall);
+ } else {
+ idtentry_exit_cond_rcu(regs, rcu_exit);
+ }
+}
+#endif /* CONFIG_XEN_PV */
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 28d13f0..84ee014 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1298,7 +1298,10 @@ SYM_CODE_END(native_iret)
#endif

#ifdef CONFIG_XEN_PV
-SYM_FUNC_START(xen_hypervisor_callback)
+/*
+ * See comment in entry_64.S for further explanation
+ */
+SYM_FUNC_START(exc_xen_hypervisor_callback)
/*
* Check to see if we got the event in the critical
* region in xen_iret_direct, after we've reenabled
@@ -1315,14 +1318,11 @@ SYM_FUNC_START(xen_hypervisor_callback)
pushl $-1 /* orig_ax = -1 => not a system call */
SAVE_ALL
ENCODE_FRAME_POINTER
- TRACE_IRQS_OFF
+
mov %esp, %eax
- call xen_evtchn_do_upcall
-#ifndef CONFIG_PREEMPTION
- call xen_maybe_preempt_hcall
-#endif
- jmp ret_from_intr
-SYM_FUNC_END(xen_hypervisor_callback)
+ call xen_pv_evtchn_do_upcall
+ jmp handle_exception_return
+SYM_FUNC_END(exc_xen_hypervisor_callback)

/*
* Hypervisor uses this for application faults while it executes.
@@ -1464,6 +1464,7 @@ SYM_CODE_START_LOCAL_NOALIGN(handle_exception)
movl %esp, %eax # pt_regs pointer
CALL_NOSPEC edi

+handle_exception_return:
#ifdef CONFIG_VM86
movl PT_EFLAGS(%esp), %eax # mix EFLAGS and CS
movb PT_CS(%esp), %al
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 6b518be..dadb37d 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1067,10 +1067,6 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt

idtentry X86_TRAP_PF page_fault do_page_fault has_error_code=1

-#ifdef CONFIG_XEN_PV
-idtentry 512 /* dummy */ hypervisor_callback xen_do_hypervisor_callback has_error_code=0
-#endif
-
/*
* Reload gs selector with exception handling
* edi: new selector
@@ -1158,9 +1154,10 @@ SYM_FUNC_END(asm_call_on_stack)
* So, on entry to the handler we detect whether we interrupted an
* existing activation in its critical region -- if so, we pop the current
* activation and restart the handler using the previous one.
+ *
+ * C calling convention: exc_xen_hypervisor_callback(struct *pt_regs)
*/
-/* do_hypervisor_callback(struct *pt_regs) */
-SYM_CODE_START_LOCAL(xen_do_hypervisor_callback)
+SYM_CODE_START_LOCAL(exc_xen_hypervisor_callback)

/*
* Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will
@@ -1170,15 +1167,10 @@ SYM_CODE_START_LOCAL(xen_do_hypervisor_callback)
movq %rdi, %rsp /* we don't return, adjust the stack frame */
UNWIND_HINT_REGS

- ENTER_IRQ_STACK old_rsp=%r10
- call xen_evtchn_do_upcall
- LEAVE_IRQ_STACK
+ call xen_pv_evtchn_do_upcall

-#ifndef CONFIG_PREEMPTION
- call xen_maybe_preempt_hcall
-#endif
- jmp error_exit
-SYM_CODE_END(xen_do_hypervisor_callback)
+ jmp error_return
+SYM_CODE_END(exc_xen_hypervisor_callback)

/*
* Hypervisor uses this for application faults while it executes.
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index b056889..49a797d 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -337,6 +337,13 @@ __visible noinstr void func(struct pt_regs *regs, \
* This avoids duplicate defines and ensures that everything is consistent.
*/

+/*
+ * Dummy trap number so the low level ASM macro vector number checks do not
+ * match which results in emitting plain IDTENTRY stubs without bells and
+ * whistels.
+ */
+#define X86_TRAP_OTHER 0xFFFF
+
/* Simple exception entry points. No hardware error code */
DECLARE_IDTENTRY(X86_TRAP_DE, exc_divide_error);
DECLARE_IDTENTRY(X86_TRAP_OF, exc_overflow);
@@ -376,4 +383,10 @@ DECLARE_IDTENTRY_XEN(X86_TRAP_DB, debug);
/* #DF */
DECLARE_IDTENTRY_DF(X86_TRAP_DF, exc_double_fault);

+#ifdef CONFIG_XEN_PV
+DECLARE_IDTENTRY(X86_TRAP_OTHER, exc_xen_hypervisor_callback);
+#endif
+
+#undef X86_TRAP_OTHER
+
#endif
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 1a2d8a5..3566e37 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -20,6 +20,7 @@
#include <asm/setup.h>
#include <asm/acpi.h>
#include <asm/numa.h>
+#include <asm/idtentry.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>

@@ -993,7 +994,8 @@ static void __init xen_pvmmu_arch_setup(void)
HYPERVISOR_vm_assist(VMASST_CMD_enable,
VMASST_TYPE_pae_extended_cr3);

- if (register_callback(CALLBACKTYPE_event, xen_hypervisor_callback) ||
+ if (register_callback(CALLBACKTYPE_event,
+ xen_asm_exc_xen_hypervisor_callback) ||
register_callback(CALLBACKTYPE_failsafe, xen_failsafe_callback))
BUG();

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 8fb8a50..a92259d 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -27,6 +27,7 @@
#include <asm/paravirt.h>
#include <asm/desc.h>
#include <asm/pgtable.h>
+#include <asm/idtentry.h>
#include <asm/cpu.h>

#include <xen/interface/xen.h>
@@ -347,7 +348,7 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
ctxt->gs_base_kernel = per_cpu_offset(cpu);
#endif
ctxt->event_callback_eip =
- (unsigned long)xen_hypervisor_callback;
+ (unsigned long)xen_asm_exc_xen_hypervisor_callback;
ctxt->failsafe_callback_eip =
(unsigned long)xen_failsafe_callback;
per_cpu(xen_cr3, cpu) = __pa(swapper_pg_dir);
diff --git a/arch/x86/xen/xen-asm_32.S b/arch/x86/xen/xen-asm_32.S
index 812ff01..d0ff2dc 100644
--- a/arch/x86/xen/xen-asm_32.S
+++ b/arch/x86/xen/xen-asm_32.S
@@ -93,7 +93,7 @@ xen_iret_start_crit:

/*
* If there's something pending, mask events again so we can
- * jump back into xen_hypervisor_callback. Otherwise do not
+ * jump back into exc_xen_hypervisor_callback. Otherwise do not
* touch XEN_vcpu_info_mask.
*/
jne 1f
@@ -113,7 +113,7 @@ iret_restore_end:
* Events are masked, so jumping out of the critical region is
* OK.
*/
- je xen_hypervisor_callback
+ je asm_exc_xen_hypervisor_callback

1: iret
xen_iret_end_crit:
@@ -127,7 +127,7 @@ SYM_CODE_END(xen_iret)
.globl xen_iret_start_crit, xen_iret_end_crit

/*
- * This is called by xen_hypervisor_callback in entry_32.S when it sees
+ * This is called by exc_xen_hypervisor_callback in entry_32.S when it sees
* that the EIP at the time of interrupt was between
* xen_iret_start_crit and xen_iret_end_crit.
*
@@ -144,7 +144,7 @@ SYM_CODE_END(xen_iret)
* eflags }
* cs } nested exception info
* eip }
- * return address : (into xen_hypervisor_callback)
+ * return address : (into asm_exc_xen_hypervisor_callback)
*
* In order to deliver the nested exception properly, we need to discard the
* nested exception frame such that when we handle the exception, we do it
@@ -152,7 +152,8 @@ SYM_CODE_END(xen_iret)
*
* The only caveat is that if the outer eax hasn't been restored yet (i.e.
* it's still on stack), we need to restore its value here.
- */
+*/
+.pushsection .noinstr.text, "ax"
SYM_CODE_START(xen_iret_crit_fixup)
/*
* Paranoia: Make sure we're really coming from kernel space.
@@ -181,3 +182,4 @@ SYM_CODE_START(xen_iret_crit_fixup)
2:
ret
SYM_CODE_END(xen_iret_crit_fixup)
+.popsection
diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index e46d863..19fbbdb 100644
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -54,7 +54,7 @@ xen_pv_trap asm_exc_simd_coprocessor_error
#ifdef CONFIG_IA32_EMULATION
xen_pv_trap entry_INT80_compat
#endif
-xen_pv_trap hypervisor_callback
+xen_pv_trap asm_exc_xen_hypervisor_callback

__INIT
SYM_CODE_START(xen_early_idt_handler_array)
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 1cc1568..ad05d05 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -8,7 +8,6 @@
#include <xen/xen-ops.h>

/* These are code, but not functions. Defined in entry.S */
-extern const char xen_hypervisor_callback[];
extern const char xen_failsafe_callback[];

void xen_sysenter_target(void);
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 0c4efa6..0d322f3 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -1,6 +1,6 @@
# SPDX-License-Identifier: GPL-2.0
obj-$(CONFIG_HOTPLUG_CPU) += cpu_hotplug.o
-obj-y += grant-table.o features.o balloon.o manage.o preempt.o time.o
+obj-y += grant-table.o features.o balloon.o manage.o time.o
obj-y += mem-reservation.o
obj-y += events/
obj-y += xenbus/
diff --git a/drivers/xen/preempt.c b/drivers/xen/preempt.c
deleted file mode 100644
index 17240c5..0000000
--- a/drivers/xen/preempt.c
+++ /dev/null
@@ -1,42 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- * Preemptible hypercalls
- *
- * Copyright (C) 2014 Citrix Systems R&D ltd.
- */
-
-#include <linux/sched.h>
-#include <xen/xen-ops.h>
-
-#ifndef CONFIG_PREEMPTION
-
-/*
- * Some hypercalls issued by the toolstack can take many 10s of
- * seconds. Allow tasks running hypercalls via the privcmd driver to
- * be voluntarily preempted even if full kernel preemption is
- * disabled.
- *
- * Such preemptible hypercalls are bracketed by
- * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
- * calls.
- */
-
-DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
-EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
-
-asmlinkage __visible void xen_maybe_preempt_hcall(void)
-{
- if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
- && need_resched())) {
- /*
- * Clear flag as we may be rescheduled on a different
- * cpu.
- */
- __this_cpu_write(xen_in_preemptible_hcall, false);
- local_irq_enable();
- cond_resched();
- local_irq_disable();
- __this_cpu_write(xen_in_preemptible_hcall, true);
- }
-}
-#endif /* CONFIG_PREEMPTION */
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index 095be1d..39a5580 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -215,17 +215,7 @@ bool xen_running_on_version_or_later(unsigned int major, unsigned int minor);
void xen_efi_runtime_setup(void);


-#ifdef CONFIG_PREEMPTION
-
-static inline void xen_preemptible_hcall_begin(void)
-{
-}
-
-static inline void xen_preemptible_hcall_end(void)
-{
-}
-
-#else
+#if defined(CONFIG_XEN_PV) && !defined(CONFIG_PREEMPTION)

DECLARE_PER_CPU(bool, xen_in_preemptible_hcall);

@@ -239,6 +229,11 @@ static inline void xen_preemptible_hcall_end(void)
__this_cpu_write(xen_in_preemptible_hcall, false);
}

-#endif /* CONFIG_PREEMPTION */
+#else
+
+static inline void xen_preemptible_hcall_begin(void) { }
+static inline void xen_preemptible_hcall_end(void) { }
+
+#endif /* CONFIG_XEN_PV && !CONFIG_PREEMPTION */

#endif /* INCLUDE_XEN_OPS_H */