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From: Khalid Aziz <khalid.aziz@oracle.com>
To: Dave Hansen <dave.hansen@intel.com>,
	juergh@gmail.com, tycho@tycho.ws, jsteckli@amazon.de,
	ak@linux.intel.com, torvalds@linux-foundation.org,
	liran.alon@oracle.com, keescook@google.com,
	akpm@linux-foundation.org, mhocko@suse.com,
	catalin.marinas@arm.com, will.deacon@arm.com, jmorris@namei.org,
	konrad.wilk@oracle.com
Cc: deepa.srinivasan@oracle.com, chris.hyser@oracle.com,
	tyhicks@canonical.com, dwmw@amazon.co.uk,
	andrew.cooper3@citrix.com, jcm@redhat.com,
	boris.ostrovsky@oracle.com, kanth.ghatraju@oracle.com,
	joao.m.martins@oracle.com, jmattson@google.com,
	pradeep.vincent@oracle.com, john.haxby@oracle.com,
	tglx@linutronix.de, kirill.shutemov@linux.intel.com, hch@lst.de,
	steven.sistare@oracle.com, labbott@redhat.com, luto@kernel.org,
	peterz@infradead.org, kernel-hardening@lists.openwall.com,
	linux-mm@kvack.org, x86@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v8 13/14] xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only)
Date: Thu, 14 Feb 2019 12:57:30 -0700	[thread overview]
Message-ID: <95fb62d4-1dbc-e420-74c1-ff929c5552e1@oracle.com> (raw)
In-Reply-To: <a6510fa8-e96d-677b-78df-da9a19c4089b@intel.com>

On 2/14/19 10:42 AM, Dave Hansen wrote:
>>  #endif
>> +
>> +	/* If there is a pending TLB flush for this CPU due to XPFO
>> +	 * flush, do it now.
>> +	 */
> 
> Don't forget CodingStyle in all this, please.

Of course. I will fix that.

> 
>> +	if (cpumask_test_and_clear_cpu(cpu, &pending_xpfo_flush)) {
>> +		count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
>> +		__flush_tlb_all();
>> +	}
> 
> This seems to exist in parallel with all of the cpu_tlbstate
> infrastructure.  Shouldn't it go in there?

That sounds like a good idea. On the other hand, pending flush needs to
be kept track of entirely within arch/x86/mm/tlb.c and using a local
variable with scope limited to just that file feels like a lighter
weight implementation. I could go either way.

> 
> Also, if we're doing full flushes like this, it seems a bit wasteful to
> then go and do later things like invalidate_user_asid() when we *know*
> that the asid would have been flushed by this operation.  I'm pretty
> sure this isn't the only __flush_tlb_all() callsite that does this, so
> it's not really criticism of this patch specifically.  It's more of a
> structural issue.
> 
> 

That is a good point. It is not just wasteful, it is bound to have
performance impact even if slight.

>> +void xpfo_flush_tlb_kernel_range(unsigned long start, unsigned long end)
>> +{
> 
> This is a bit lightly commented.  Please give this some good
> descriptions about the logic behind the implementation and the tradeoffs
> that are in play.
> 
> This is doing a local flush, but deferring the flushes on all other
> processors, right?  Can you explain the logic behind that in a comment
> here, please?  This also has to be called with preemption disabled, right?
> 
>> +	struct cpumask tmp_mask;
>> +
>> +	/* Balance as user space task's flush, a bit conservative */
>> +	if (end == TLB_FLUSH_ALL ||
>> +	    (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) {
>> +		do_flush_tlb_all(NULL);
>> +	} else {
>> +		struct flush_tlb_info info;
>> +
>> +		info.start = start;
>> +		info.end = end;
>> +		do_kernel_range_flush(&info);
>> +	}
>> +	cpumask_setall(&tmp_mask);
>> +	cpumask_clear_cpu(smp_processor_id(), &tmp_mask);
>> +	cpumask_or(&pending_xpfo_flush, &pending_xpfo_flush, &tmp_mask);
>> +}
> 
> Fun.  cpumask_setall() is non-atomic while cpumask_clear_cpu() and
> cpumask_or() *are* atomic.  The cpumask_clear_cpu() is operating on
> thread-local storage and doesn't need to be atomic.  Please make it
> __cpumask_clear_cpu().
> 

I will fix that. Thanks!

--
Khalid

  reply	other threads:[~2019-02-14 19:57 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-14  0:01 [RFC PATCH v8 00/14] Add support for eXclusive Page Frame Ownership Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 01/14] mm: add MAP_HUGETLB support to vm_mmap Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 02/14] x86: always set IF before oopsing from page fault Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 03/14] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Khalid Aziz
2019-02-14 10:56   ` Peter Zijlstra
2019-02-14 16:15     ` Borislav Petkov
2019-02-14 17:19       ` Khalid Aziz
2019-02-14 17:13     ` Khalid Aziz
2019-02-14 19:08       ` Peter Zijlstra
2019-02-14 19:58         ` Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 04/14] swiotlb: Map the buffer if it was unmapped by XPFO Khalid Aziz
2019-02-14  7:47   ` Christoph Hellwig
2019-02-14 16:56     ` Khalid Aziz
2019-02-14 17:44       ` Christoph Hellwig
2019-02-14 19:48         ` Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 05/14] arm64/mm: Add support for XPFO Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 06/14] xpfo: add primitives for mapping underlying memory Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 07/14] arm64/mm, xpfo: temporarily map dcache regions Khalid Aziz
2019-02-14 15:54   ` Tycho Andersen
2019-02-14 17:29     ` Khalid Aziz
2019-02-14 23:49       ` Tycho Andersen
2019-02-14  0:01 ` [RFC PATCH v8 08/14] arm64/mm: disable section/contiguous mappings if XPFO is enabled Khalid Aziz
2019-02-15 13:09   ` Mark Rutland
2019-02-15 14:47     ` Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 09/14] mm: add a user_virt_to_phys symbol Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 10/14] lkdtm: Add test for XPFO Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 11/14] xpfo, mm: remove dependency on CONFIG_PAGE_EXTENSION Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 12/14] xpfo, mm: optimize spinlock usage in xpfo_kunmap Khalid Aziz
2019-02-14  0:01 ` [RFC PATCH v8 13/14] xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only) Khalid Aziz
2019-02-14 17:42   ` Dave Hansen
2019-02-14 19:57     ` Khalid Aziz [this message]
2019-02-14  0:01 ` [RFC PATCH v8 14/14] xpfo, mm: Optimize XPFO TLB flushes by batching them together Khalid Aziz

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