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Subject[PATCH 1/2] x86/context-tracking: Remove exception_enter/exit() from do_page_fault()
Date
do_page_fault(), like other exceptions, is already covered by
user_enter() and user_exit() when the exception triggers in userspace.

As explained in 8c84014f3bbb112d07e73f30a10ac8a3a72f8649
("x86/entry: Remove exception_enter() from most trap handlers"),
exception_enter/exit() only remained to handle possible page fault from
kernel mode while context tracking is in CONTEXT_USER mode, ie: on
kernel entry before we manage to call user_exit(). And the only known
offender was do_fast_syscall_32() fetching EBP register from where
vDSO stashed it.

Meanwhile this got fixed with 9999c8c01f34c918a57d6e5ba2f5d8b79aa04801
("x86/entry: Call enter_from_user_mode() with IRQs off") that moved
enter_from_user_mode() before the call to get_user().

So we can safely remove it now.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
---
arch/x86/mm/fault.c | 39 ++++++++++++---------------------------
1 file changed, 12 insertions(+), 27 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 304d31d8cbbc..2b4ab2862eda 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1486,27 +1486,6 @@ void do_user_addr_fault(struct pt_regs *regs,
}
NOKPROBE_SYMBOL(do_user_addr_fault);

-/*
- * Explicitly marked noinline such that the function tracer sees this as the
- * page_fault entry point.
- */
-static noinline void
-__do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
- unsigned long address)
-{
- prefetchw(&current->mm->mmap_sem);
-
- 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, hw_error_code, address);
- else
- do_user_addr_fault(regs, hw_error_code, address);
-}
-NOKPROBE_SYMBOL(__do_page_fault);
-
static __always_inline void
trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
@@ -1521,13 +1500,19 @@ trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
}

dotraplinkage void
-do_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address)
+do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
+ unsigned long address)
{
- enum ctx_state prev_state;
+ prefetchw(&current->mm->mmap_sem);
+ trace_page_fault_entries(regs, hw_error_code, address);

- prev_state = exception_enter();
- trace_page_fault_entries(regs, error_code, address);
- __do_page_fault(regs, error_code, address);
- exception_exit(prev_state);
+ 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, hw_error_code, address);
+ else
+ do_user_addr_fault(regs, hw_error_code, address);
}
NOKPROBE_SYMBOL(do_page_fault);
--
2.23.0
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