[patch V5 13/38] x86/entry: Switch page fault exception to IDTENTRY_RAW

From: Thomas Gleixner
Date: Tue May 12 2020 - 18:23:19 EST

Convert page fault exceptions to IDTENTRY_RAW:
- Implement the C entry point with DEFINE_IDTENTRY_RAW
- Add the CR2 read into the exception handler
- Add the idtentry_enter/exit_cond_rcu() invocations in
in the regular page fault handler and use the regular
idtentry_enter/exit() for the async PF part.
- Emit the ASM stub with DECLARE_IDTENTRY_RAW
- Remove the ASM idtentry in 64bit
- Remove the CR2 read from 64bit
- Remove the open coded ASM entry code in 32bit
- Fixup the XEN/PV code
- Remove the old prototypes

No functional change.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/x86/entry/entry_32.S | 30 -----------------
arch/x86/entry/entry_64.S | 19 -----------
arch/x86/include/asm/idtentry.h | 3 +
arch/x86/include/asm/traps.h | 11 ------
arch/x86/kernel/idt.c | 4 +-
arch/x86/kernel/kvm.c | 14 ++++----
arch/x86/mm/fault.c | 69 +++++++++++++++++++++++++++-------------
arch/x86/xen/enlighten_pv.c | 2 -
arch/x86/xen/xen-asm_64.S | 2 -
9 files changed, 62 insertions(+), 92 deletions(-)

--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1395,36 +1395,6 @@ BUILD_INTERRUPT3(hv_stimer0_callback_vec

#endif /* CONFIG_HYPERV */

-SYM_CODE_START(page_fault)
- ASM_CLAC
- pushl $do_page_fault
- jmp common_exception_read_cr2
-SYM_CODE_END(page_fault)
-
-SYM_CODE_START_LOCAL_NOALIGN(common_exception_read_cr2)
- /* the function address is in %gs's slot on the stack */
- SAVE_ALL switch_stacks=1 skip_gs=1 unwind_espfix=1
-
- ENCODE_FRAME_POINTER
-
- /* fixup %gs */
- GS_TO_REG %ecx
- movl PT_GS(%esp), %edi
- REG_TO_PTGS %ecx
- SET_KERNEL_GS %ecx
-
- GET_CR2_INTO(%ecx) # might clobber %eax
-
- /* fixup orig %eax */
- movl PT_ORIG_EAX(%esp), %edx # get the error code
- movl $-1, PT_ORIG_EAX(%esp) # no syscall to restart
-
- TRACE_IRQS_OFF
- movl %esp, %eax # pt_regs pointer
- CALL_NOSPEC edi
- jmp ret_from_exception
-SYM_CODE_END(common_exception_read_cr2)
-
SYM_CODE_START_LOCAL_NOALIGN(common_exception)
/* the function address is in %gs's slot on the stack */
SAVE_ALL switch_stacks=1 skip_gs=1 unwind_espfix=1
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -507,15 +507,6 @@ SYM_CODE_END(spurious_entries_start)
call error_entry
UNWIND_HINT_REGS

- .if \vector == X86_TRAP_PF
- /*
- * Store CR2 early so subsequent faults cannot clobber it. Use R12 as
- * intermediate storage as RDX can be clobbered in enter_from_user_mode().
- * GET_CR2_INTO can clobber RAX.
- */
- GET_CR2_INTO(%r12);
- .endif
-
.if \sane == 0
TRACE_IRQS_OFF

@@ -534,10 +525,6 @@ SYM_CODE_END(spurious_entries_start)
movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */
.endif

- .if \vector == X86_TRAP_PF
- movq %r12, %rdx /* Move CR2 into 3rd argument */
- .endif
-
call \cfunc

.if \sane == 0
@@ -1060,12 +1047,6 @@ apicinterrupt IRQ_WORK_VECTOR irq_work
#endif

/*
- * Exception entry points.
- */
-
-idtentry X86_TRAP_PF page_fault do_page_fault has_error_code=1
-
-/*
* Reload gs selector with exception handling
* edi: new selector
*
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -364,7 +364,8 @@ DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_GP,
DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_AC, exc_alignment_check);

/* Raw exception entries which need extra work */
-DECLARE_IDTENTRY_RAW(X86_TRAP_BP, exc_int3);
+DECLARE_IDTENTRY_RAW(X86_TRAP_BP, exc_int3);
+DECLARE_IDTENTRY_RAW_ERRORCODE(X86_TRAP_PF, exc_page_fault);

#ifdef CONFIG_X86_MCE
DECLARE_IDTENTRY_MCE(X86_TRAP_MC, exc_machine_check);
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -9,17 +9,6 @@
#include <asm/idtentry.h>
#include <asm/siginfo.h> /* TRAP_TRACE, ... */

-#define dotraplinkage __visible
-
-asmlinkage void page_fault(void);
-asmlinkage void async_page_fault(void);
-
-#if defined(CONFIG_X86_64) && defined(CONFIG_XEN_PV)
-asmlinkage void xen_page_fault(void);
-#endif
-
-dotraplinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address);
-
#ifdef CONFIG_X86_64
asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs);
asmlinkage __visible notrace
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -59,7 +59,7 @@ static const __initconst struct idt_data
INTG(X86_TRAP_DB, asm_exc_debug),
SYSG(X86_TRAP_BP, asm_exc_int3),
#ifdef CONFIG_X86_32
- INTG(X86_TRAP_PF, page_fault),
+ INTG(X86_TRAP_PF, asm_exc_page_fault),
#endif
};

@@ -153,7 +153,7 @@ static const __initconst struct idt_data
* stacks work only after cpu_init().
*/
static const __initconst struct idt_data early_pf_idts[] = {
- INTG(X86_TRAP_PF, page_fault),
+ INTG(X86_TRAP_PF, asm_exc_page_fault),
};

/*
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -218,7 +218,7 @@ void kvm_async_pf_task_wake(u32 token)
}
EXPORT_SYMBOL_GPL(kvm_async_pf_task_wake);

-u32 kvm_read_and_reset_pf_reason(void)
+u32 noinstr kvm_read_and_reset_pf_reason(void)
{
u32 reason = 0;

@@ -230,9 +230,8 @@ u32 kvm_read_and_reset_pf_reason(void)
return reason;
}
EXPORT_SYMBOL_GPL(kvm_read_and_reset_pf_reason);
-NOKPROBE_SYMBOL(kvm_read_and_reset_pf_reason);

-bool __kvm_handle_async_pf(struct pt_regs *regs, u32 token)
+noinstr bool __kvm_handle_async_pf(struct pt_regs *regs, u32 token)
{
u32 reason = kvm_read_and_reset_pf_reason();

@@ -244,6 +243,9 @@ bool __kvm_handle_async_pf(struct pt_reg
return false;
}

+ idtentry_enter(regs);
+ instrumentation_begin();
+
/*
* If the host managed to inject an async #PF into an interrupt
* disabled region, then die hard as this is not going to end well
@@ -258,13 +260,13 @@ bool __kvm_handle_async_pf(struct pt_reg
/* Page is swapped out by the host. */
kvm_async_pf_task_wait_schedule(token);
} else {
- rcu_irq_enter();
kvm_async_pf_task_wake(token);
- rcu_irq_exit();
}
+
+ instrumentation_end();
+ idtentry_exit(regs);
return true;
}
-NOKPROBE_SYMBOL(__kvm_handle_async_pf);

static void __init paravirt_ops_setup(void)
{
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1521,11 +1521,38 @@ trace_page_fault_entries(struct pt_regs
trace_page_fault_kernel(address, regs, error_code);
}

-dotraplinkage void
-do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
- unsigned long address)
+static __always_inline void
+handle_page_fault(struct pt_regs *regs, unsigned long error_code,
+ unsigned long address)
{
+ trace_page_fault_entries(regs, error_code, address);
+
+ if (unlikely(kmmio_fault(regs, address)))
+ return;
+
+ /* Was the fault on kernel-controlled part of the address space? */
+ if (unlikely(fault_in_kernel_space(address))) {
+ do_kern_addr_fault(regs, error_code, address);
+ } else {
+ do_user_addr_fault(regs, error_code, address);
+ /*
+ * User address page fault handling might have reenabled
+ * interrupts. Fixing up all potential exit points of
+ * do_user_addr_fault() and its leaf functions is just not
+ * doable w/o creating an unholy mess or turning the code
+ * upside down.
+ */
+ local_irq_disable();
+ }
+}
+
+DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
+{
+ unsigned long address = read_cr2();
+ bool rcu_exit;
+
prefetchw(&current->mm->mmap_sem);
+
/*
* KVM has two types of events that are, logically, interrupts, but
* are unfortunately delivered using the #PF vector. These events are
@@ -1540,28 +1567,28 @@ do_page_fault(struct pt_regs *regs, unsi
* getting values from real and async page faults mixed up.
*
* Fingers crossed.
+ *
+ * The async #PF handling code takes care of idtentry handling
+ * itself.
*/
if (kvm_handle_async_pf(regs, (u32)address))
return;

- trace_page_fault_entries(regs, hw_error_code, address);
+ /*
+ * Entry handling for valid #PF from kernel mode is slightly
+ * different: RCU is already watching and rcu_irq_enter() must not
+ * be invoked because a kernel fault on a user space address might
+ * sleep.
+ *
+ * In case the fault hit a RCU idle region the conditional entry
+ * code reenabled RCU to avoid subsequent wreckage which helps
+ * debugability.
+ */
+ rcu_exit = idtentry_enter_cond_rcu(regs);

- if (unlikely(kmmio_fault(regs, address)))
- return;
+ instrumentation_begin();
+ handle_page_fault(regs, error_code, address);
+ instrumentation_end();

- /* Was the fault on kernel-controlled part of the address space? */
- if (unlikely(fault_in_kernel_space(address))) {
- do_kern_addr_fault(regs, hw_error_code, address);
- } else {
- do_user_addr_fault(regs, hw_error_code, address);
- /*
- * User address page fault handling might have reenabled
- * interrupts. Fixing up all potential exit points of
- * do_user_addr_fault() and its leaf functions is just not
- * doable w/o creating an unholy mess or turning the code
- * upside down.
- */
- local_irq_disable();
- }
+ idtentry_exit_cond_rcu(regs, rcu_exit);
}
-NOKPROBE_SYMBOL(do_page_fault);
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -627,7 +627,7 @@ static struct trap_array_entry trap_arra
#ifdef CONFIG_IA32_EMULATION
{ entry_INT80_compat, xen_entry_INT80_compat, false },
#endif
- { page_fault, xen_page_fault, false },
+ TRAP_ENTRY(exc_page_fault, false ),
TRAP_ENTRY(exc_divide_error, false ),
TRAP_ENTRY(exc_bounds, false ),
TRAP_ENTRY(exc_invalid_op, false ),
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -43,7 +43,7 @@ xen_pv_trap asm_exc_invalid_tss
xen_pv_trap asm_exc_segment_not_present
xen_pv_trap asm_exc_stack_segment
xen_pv_trap asm_exc_general_protection
-xen_pv_trap page_fault
+xen_pv_trap asm_exc_page_fault
xen_pv_trap asm_exc_spurious_interrupt_bug
xen_pv_trap asm_exc_coprocessor_error
xen_pv_trap asm_exc_alignment_check