From: Zhenzhong Duan <zhenzhong.duan@oracle.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>, linux-kernel@vger.kernel.org
Cc: Juergen Gross <jgross@suse.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org, srinivas.eeda@oracle.com,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Andy Lutomirski <luto@kernel.org>,
xen-devel@lists.xenproject.org,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [Xen-devel] [PATCH v2] xen/pv: Fix a boot up hang revealed by int3 self test
Date: Mon, 15 Jul 2019 13:05:13 +0800 [thread overview]
Message-ID: <b9702975-dd2d-cf0b-e47f-a1c4361db18f@oracle.com> (raw)
In-Reply-To: <ebf9657b-7d97-87a0-e32e-af8453ee7bba@citrix.com>
On 2019/7/12 22:06, Andrew Cooper wrote:
> On 11/07/2019 03:15, Zhenzhong Duan wrote:
>> Commit 7457c0da024b ("x86/alternatives: Add int3_emulate_call()
>> selftest") is used to ensure there is a gap setup in exception stack
>> which could be used for inserting call return address.
>>
>> This gap is missed in XEN PV int3 exception entry path, then below panic
>> triggered:
>>
>> [ 0.772876] general protection fault: 0000 [#1] SMP NOPTI
>> [ 0.772886] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0+ #11
>> [ 0.772893] RIP: e030:int3_magic+0x0/0x7
>> [ 0.772905] RSP: 3507:ffffffff82203e98 EFLAGS: 00000246
>> [ 0.773334] Call Trace:
>> [ 0.773334] alternative_instructions+0x3d/0x12e
>> [ 0.773334] check_bugs+0x7c9/0x887
>> [ 0.773334] ? __get_locked_pte+0x178/0x1f0
>> [ 0.773334] start_kernel+0x4ff/0x535
>> [ 0.773334] ? set_init_arg+0x55/0x55
>> [ 0.773334] xen_start_kernel+0x571/0x57a
>>
>> As xenint3 and int3 entry code are same except xenint3 doesn't generate
>> a gap, we can fix it by using int3 and drop useless xenint3.
> For 64bit PV guests, Xen's ABI enters the kernel with using SYSRET, with
> %rcx/%r11 on the stack.
>
> To convert back to "normal" looking exceptions, the xen thunks do `pop
> %rcx; pop %r11; jmp do_*`...
I will add this to commit message.
>
>> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
>> index 0ea4831..35a66fc 100644
>> --- a/arch/x86/entry/entry_64.S
>> +++ b/arch/x86/entry/entry_64.S
>> @@ -1176,7 +1176,6 @@ idtentry stack_segment do_stack_segment has_error_code=1
>> #ifdef CONFIG_XEN_PV
>> idtentry xennmi do_nmi has_error_code=0
>> idtentry xendebug do_debug has_error_code=0
>> -idtentry xenint3 do_int3 has_error_code=0
>> #endif
> What is confusing is why there are 3 extra magic versions here. At a
> guess, I'd say something to do with IST settings (given the vectors),
> but I don't see why #DB/#BP would need to be different in the first
> place. (NMI sure, but that is more to do with the crazy hoops needing
> to be jumped through to keep native functioning safely.)
xenint3 will be removed in this patch safely as it don't use IST now.
But debug and nmi need paranoid_entry which will read MSR_GS_BASE to
determine
if swapgs is needed. I guess PV guesting running in ring3 will #GP with
swapgs?
Zhenzhong
next prev parent reply other threads:[~2019-07-15 5:06 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-11 8:15 [PATCH v2] xen/pv: Fix a boot up hang revealed by int3 self test Zhenzhong Duan
2019-07-12 12:06 ` Peter Zijlstra
2019-07-12 13:04 ` Zhenzhong Duan
2019-07-12 13:09 ` Peter Zijlstra
2019-07-12 13:17 ` Peter Zijlstra
2019-07-12 13:27 ` Zhenzhong Duan
2019-07-12 14:06 ` [Xen-devel] " Andrew Cooper
2019-07-15 5:05 ` Zhenzhong Duan [this message]
2019-07-15 6:54 ` Jan Beulich
2019-07-15 9:09 ` Andrew Cooper
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