From: Dave Hansen <dave.hansen@linux.intel.com>
To: linux-kernel@vger.kernel.org
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
sean.j.christopherson@intel.com, peterz@infradead.org,
tglx@linutronix.de, x86@kernel.org, luto@kernel.org
Subject: [RFC][PATCH 8/8] x86/mm: remove spurious fault pkey check
Date: Fri, 07 Sep 2018 12:49:04 -0700 [thread overview]
Message-ID: <20180907194904.3333BC92@viggo.jf.intel.com> (raw)
In-Reply-To: <20180907194852.3C351B82@viggo.jf.intel.com>
From: Dave Hansen <dave.hansen@linux.intel.com>
Spurious faults only ever occur in the kernel's address space. They
are also constrained specifically to faults with one of these error codes:
X86_PF_WRITE | X86_PF_PROT
X86_PF_INSTR | X86_PF_PROT
So, it's never even possible to reach spurious_kernel_fault_check() with
X86_PF_PK set.
In addition, the kernel's address space never has pages with user-mode
protections. Protection Keys are only enforced on pages with user-mode
protection.
This gives us lots of reasons to not check for protection keys in our
sprurious kernel fault handling.
But, let's also add some warnings to ensure that these assumptions about
protection keys hold true.
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Cc: Andy Lutomirski <luto@kernel.org>
---
b/arch/x86/mm/fault.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff -puN arch/x86/mm/fault.c~pkeys-fault-warnings arch/x86/mm/fault.c
--- a/arch/x86/mm/fault.c~pkeys-fault-warnings 2018-09-07 12:32:23.190741335 -0700
+++ b/arch/x86/mm/fault.c 2018-09-07 12:32:23.194741335 -0700
@@ -1037,12 +1037,6 @@ static int spurious_kernel_fault_check(u
if ((error_code & X86_PF_INSTR) && !pte_exec(*pte))
return 0;
- /*
- * Note: We do not do lazy flushing on protection key
- * changes, so no spurious fault will ever set X86_PF_PK.
- */
- if ((error_code & X86_PF_PK))
- return 1;
return 1;
}
@@ -1213,6 +1207,13 @@ do_kern_addr_space_fault(struct pt_regs
unsigned long address)
{
/*
+ * Protection keys exceptions only happen on user pages. We
+ * have no user pages in the kernel portion of the address
+ * space, so do not expect them here.
+ */
+ WARN_ON_ONCE(hw_error_code & X86_PF_PK);
+
+ /*
* We can fault-in kernel-space virtual memory on-demand. The
* 'reference' page table is init_mm.pgd.
*
_
prev parent reply other threads:[~2018-09-07 19:51 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-07 19:48 [RFC][PATCH 0/8] x86/mm: page fault handling cleanups Dave Hansen
2018-09-07 19:48 ` [RFC][PATCH 1/8] x86/mm: clarify hardware vs. software "error_code" Dave Hansen
2018-09-07 22:48 ` Andy Lutomirski
2018-09-10 20:07 ` Dave Hansen
2018-09-10 21:17 ` Andy Lutomirski
2018-09-07 19:48 ` [RFC][PATCH 2/8] x86/mm: break out kernel address space handling Dave Hansen
2018-09-07 21:06 ` Sean Christopherson
2018-09-07 21:51 ` Dave Hansen
2018-09-07 22:21 ` Andy Lutomirski
2018-09-07 22:37 ` Dave Hansen
2018-09-07 19:48 ` [RFC][PATCH 3/8] x86/mm: break out user " Dave Hansen
2018-09-08 9:38 ` Peter Zijlstra
2018-09-10 20:20 ` Dave Hansen
2018-09-07 19:48 ` [RFC][PATCH 4/8] x86/mm: add clarifying comments for user addr space Dave Hansen
2018-09-07 19:49 ` [RFC][PATCH 5/8] x86/mm: fix exception table comments Dave Hansen
2018-09-07 21:04 ` Sean Christopherson
2018-09-07 21:51 ` Dave Hansen
2018-09-10 20:43 ` Sean Christopherson
2018-09-08 0:37 ` Jann Horn
2018-09-07 19:49 ` [RFC][PATCH 6/8] x86/mm: add vsyscall address helper Dave Hansen
2018-09-08 0:46 ` Jann Horn
2018-09-07 19:49 ` [RFC][PATCH 7/8] x86/mm/vsyscall: consider vsyscall page part of user address space Dave Hansen
2018-09-07 22:58 ` Andy Lutomirski
2018-09-08 1:16 ` Jann Horn
2018-09-07 19:49 ` Dave Hansen [this message]
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