From: Daniel Borkmann <daniel@iogearbox•net>
To: Linus Torvalds <torvalds@linux-foundation•org>
Cc: Thomas Gleixner <tglx@linutronix•de>,
Kees Cook <keescook@chromium•org>,
Laura Abbott <labbott@redhat•com>, Ingo Molnar <mingo@kernel•org>,
Peter Anvin <hpa@zytor•com>,
Fengguang Wu <fengguang.wu@intel•com>,
Network Development <netdev@vger•kernel.org>,
LKML <linux-kernel@vger•kernel.org>, LKP <lkp@01•org>,
ast@fb•com, the arch/x86 maintainers <x86@kernel•org>,
"David S. Miller" <davem@davemloft•net>,
bp@suse•de
Subject: Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request at 0000a7cf
Date: Thu, 09 Mar 2017 22:32:12 +0100 [thread overview]
Message-ID: <58C1C9DC.7070509@iogearbox.net> (raw)
In-Reply-To: <58C19F67.3040509@iogearbox.net>
[ + Borislav ]
On 03/09/2017 07:31 PM, Daniel Borkmann wrote:
> On 03/09/2017 07:15 PM, Linus Torvalds wrote:
>> On Thu, Mar 9, 2017 at 10:10 AM, Linus Torvalds
>> <torvalds@linux-foundation•org> wrote:
>>>
>>> Very odd. We should always have PGE (0x0080) set in cr4 (if the CPU
>>> supports it).
>>
>> Daniel, do you see the code in probe_page_size_mask() triggering?
>>
>> /* Enable PGE if available */
>> if (boot_cpu_has(X86_FEATURE_PGE)) {
>> cr4_set_bits_and_update_boot(X86_CR4_PGE);
>> __supported_pte_mask |= _PAGE_GLOBAL;
>
> We do have boot_cpu_has(X86_FEATURE_PGE) and go indeed into this
> branch here. So it seems something must be clearing it later, hmm.
>
>> } else
>> __supported_pte_mask &= ~_PAGE_GLOBAL;
>>
>> but maybe there's something wrong with the percpu cr4 caching?
So, I think I got a little bit further. To the printk's I added
previously in the test_setmem code that run on the problematic
kernel, I now extended them into:
printk("static_cpu X86_FEATURE_PGE:%u\n", static_cpu_has(X86_FEATURE_PGE));
printk("boot_cpu X86_FEATURE_PGE:%u\n", boot_cpu_has(X86_FEATURE_PGE));
printk("static_cpu X86_FEATURE_INVPCID:%u\n", static_cpu_has(X86_FEATURE_INVPCID));
printk("boot_cpu X86_FEATURE_INVPCID:%u\n", boot_cpu_has(X86_FEATURE_INVPCID));
And here's what I get in the log:
"-cpu kvm64" gives:
[ 8.426865] static_cpu X86_FEATURE_PGE:1
[ 8.427148] boot_cpu X86_FEATURE_PGE:0
[ 8.427428] static_cpu X86_FEATURE_INVPCID:0
[ 8.427732] boot_cpu X86_FEATURE_INVPCID:0
"-cpu host" gives:
[ 8.426408] static_cpu X86_FEATURE_PGE:1
[ 8.426726] boot_cpu X86_FEATURE_PGE:0
[ 8.427037] static_cpu X86_FEATURE_INVPCID:1
[ 8.427375] boot_cpu X86_FEATURE_INVPCID:1
This means at that point in time static_cpu_has(X86_FEATURE_PGE) is
not the same as boot_cpu_has(X86_FEATURE_PGE).
The code that switches this off is in lguest_arch_host_init(). Right
before that, both are X86_FEATURE_PGE:1, X86_FEATURE_INVPCID:0 for
the "-cpu kvm64" case.
Then, the lguest code does:
get_online_cpus();
if (boot_cpu_has(X86_FEATURE_PGE)) { /* We have a broader idea of "global". */
/* Remember that this was originally set (for cleanup). */
cpu_had_pge = 1;
/*
* adjust_pge is a helper function which sets or unsets the PGE
* bit on its CPU, depending on the argument (0 == unset).
*/
on_each_cpu(adjust_pge, (void *)0, 1);
/* Turn off the feature in the global feature set. */
clear_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE);
}
put_online_cpus();
So, adjust_pge() clears X86_CR4_PGE, and boot cpu has X86_FEATURE_PGE
unset. This means, with static_cpu_has(X86_FEATURE_PGE) still 1, we
run into using cr4 for TLB flushing with no X86_CR4_PGE bit set (which
doesn't trigger the flush), whereas we should be using cr3 for flushing
from that point onwards instead.
I tried with this one, and things seem to work again:
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 6fa8594..fc5abff 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -188,7 +188,7 @@ static inline void __native_flush_tlb_single(unsigned long addr)
static inline void __flush_tlb_all(void)
{
- if (static_cpu_has(X86_FEATURE_PGE))
+ if (boot_cpu_has(X86_FEATURE_PGE))
__flush_tlb_global();
else
__flush_tlb();
Presumably coming from c109bf95992b ("x86/cpufeature: Remove cpu_has_pge")?
Thanks,
Daniel
next prev parent reply other threads:[~2017-03-09 21:32 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-01 12:54 [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request at 0000a7cf Fengguang Wu
2017-03-02 20:23 ` Fengguang Wu
2017-03-02 20:40 ` Daniel Borkmann
2017-03-08 19:25 ` Linus Torvalds
2017-03-08 22:27 ` Daniel Borkmann
2017-03-08 22:36 ` Kees Cook
2017-03-08 22:51 ` Daniel Borkmann
2017-03-08 23:55 ` Laura Abbott
2017-03-09 5:36 ` Kees Cook
2017-03-09 13:04 ` Daniel Borkmann
2017-03-09 13:10 ` Thomas Gleixner
2017-03-09 13:25 ` Daniel Borkmann
2017-03-09 14:49 ` Thomas Gleixner
2017-03-09 17:51 ` Daniel Borkmann
2017-03-09 18:08 ` David Miller
2017-03-09 18:10 ` Linus Torvalds
2017-03-09 18:15 ` Linus Torvalds
2017-03-09 18:31 ` Daniel Borkmann
2017-03-09 21:32 ` Daniel Borkmann [this message]
2017-03-09 21:55 ` Borislav Petkov
2017-03-09 22:07 ` Borislav Petkov
2017-03-09 22:11 ` Daniel Borkmann
2017-03-09 22:48 ` Borislav Petkov
2017-03-09 23:26 ` Linus Torvalds
2017-03-09 23:44 ` Borislav Petkov
2017-03-10 0:13 ` Daniel Borkmann
2017-03-12 21:40 ` Borislav Petkov
2017-03-09 14:53 ` Daniel Borkmann
2017-03-09 17:48 ` Linus Torvalds
2017-03-08 22:43 ` Linus Torvalds
2017-03-09 1:34 ` Fengguang Wu
2017-03-09 13:09 ` Thomas Gleixner
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