From: "H. Peter Anvin" <hpa@zytor.com>
To: Borislav Petkov <bp@alien8.de>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Greg KH <gregkh@linuxfoundation.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
mingo@redhat.com, tglx@linutronix.de, xen-devel@lists.xen.org,
linux-kernel@vger.kernel.org, samu.kallio@aberdeencloud.com,
kraman@redhat.com, jwboyer@redhat.com
Subject: Re: Is: x86: mm: Fix vmalloc_fault oops during lazy MMU updates Was: Re: [PATCH] mm/x86: Flush lazy MMU when DEBUG_PAGEALLOC is set
Date: Thu, 28 Feb 2013 07:53:44 -0800 [thread overview]
Message-ID: <512F7D88.4090703@zytor.com> (raw)
In-Reply-To: <20130228153846.GA9782@pd.tnic>
On 02/28/2013 07:38 AM, Borislav Petkov wrote:
> On Thu, Feb 28, 2013 at 09:29:10AM -0500, Konrad Rzeszutek Wilk wrote:
>> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
>> index fb674fd..4f7d793 100644
>> --- a/arch/x86/mm/fault.c
>> +++ b/arch/x86/mm/fault.c
>> @@ -378,10 +378,12 @@ static noinline __kprobes int vmalloc_fault(unsigned long address)
>> if (pgd_none(*pgd_ref))
>> return -1;
>>
>> - if (pgd_none(*pgd))
>> + if (pgd_none(*pgd)) {
>> set_pgd(pgd, *pgd_ref);
>> - else
>> + arch_flush_lazy_mmu_mode();
>
> Do I understand it correctly that this would cost us a
> "preempt_disable(); preempt_enable()" needlessly on baremetal when
> running with CONFIG_PARAVIRT enabled?
>
OK, this is mind-boggingly crazy and these things that just drives me
batty about PV.
arch_flush_lazy_mmu_mode() involves a function call and preemption off
*before it even tests for being a noop*. On bare metal this function
doesn't do anything, and cannot do anything.
At the very least we should have an early filter for the **COMMON!**
case that we are not on a PV platform.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
next prev parent reply other threads:[~2013-02-28 15:55 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-26 23:57 [PATCH] mm/x86: Flush lazy MMU when DEBUG_PAGEALLOC is set Boris Ostrovsky
2013-02-27 22:40 ` H. Peter Anvin
2013-02-27 23:00 ` Greg KH
2013-02-27 23:07 ` H. Peter Anvin
2013-02-28 14:29 ` Is: x86: mm: Fix vmalloc_fault oops during lazy MMU updates Was: " Konrad Rzeszutek Wilk
2013-02-28 15:38 ` Borislav Petkov
2013-02-28 15:53 ` H. Peter Anvin [this message]
2013-02-28 16:10 ` Borislav Petkov
2013-02-28 16:20 ` Boris Ostrovsky
2013-02-28 16:22 ` Borislav Petkov
2013-02-28 16:24 ` H. Peter Anvin
2013-02-28 16:27 ` Boris Ostrovsky
2013-02-28 16:32 ` Borislav Petkov
2013-02-28 18:14 ` Steven Rostedt
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