linuxppc-dev.lists.ozlabs.org archive mirror
 help / color / mirror / Atom feed
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	paulus@samba.org, mpe@ellerman.id.au, ryabinin.a.a@gmail.com
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: [RFC PATCH V1 0/8] KASAN ppc64 support
Date: Mon, 17 Aug 2015 16:20:36 +0530	[thread overview]
Message-ID: <87io8ep4sj.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <1439805684.2416.16.camel@kernel.crashing.org>

Benjamin Herrenschmidt <benh@kernel.crashing.org> writes:

> On Mon, 2015-08-17 at 15:20 +0530, Aneesh Kumar K.V wrote:
>
>> For kernel linear mapping, our address space looks like
>> 0xc000000000000000 - 0xc0003fffffffffff  (64TB)
>> 
>> We can't have virtual address(effective address) above that range
>> in 0xc region. Hence in-order to shadow the linear mapping, I am 
>> using region 0xe. ie, the shadow mapping now looks liwe
>> 
>> 0xc000000000000000 -> 0xe000000000000000 
>
> Why ? IE. Why can't you put the shadow at address +64T and have it work
> for everything ?
> .../...

Above +64TB ? How will that work ? We have check in different parts of
code like below, where we check each region's top address is within 64TB range. 

PGTABLE_RANGE and (ESID_BITS + SID_SHIFT) and all dependendent on 64TB
range. (46 bits).


static inline unsigned long get_vsid(unsigned long context, unsigned long ea,
				     int ssize)
{
	/*
	 * Bad address. We return VSID 0 for that
	 */
	if ((ea & ~REGION_MASK) >= PGTABLE_RANGE)
		return 0;

	if (ssize == MMU_SEGSIZE_256M)
		return vsid_scramble((context << ESID_BITS)
				     | (ea >> SID_SHIFT), 256M);
	return vsid_scramble((context << ESID_BITS_1T)
			     | (ea >> SID_SHIFT_1T), 1T);
}



>> Another reason why inline instrumentation is difficult is that for
>> inline instrumentation to work, we need to create a mapping for 
>> _possible_
>> virtual address space before kasan is fully initialized. ie, we need
>> to create page table entries for the shadow of the entire 64TB range,
>> with zero page, even though we have lesser ram. We definitely can't 
>> bolt those entries. I am yet to get the shadow for kernel linear 
>> mapping to work without bolting. Also we will have to get the page 
>> table allocated for that, because we can't share page table entries. 
>> Our fault path use pte entries for storing hash slot index.
>
> Hrm, that means we might want to start considering a page table to
> cover the linear mapping...

But that would require us to get a large zero page ? Are you suggesting
to use 16G page ? 


>
>> If we are ok to steal part of that 64TB range, for kasan mapping , ie
>> we make shadow of each region part of the same region, may be we can
>> get inline instrumentation to work. But that still doesn't solve the
>> page table allocation overhead issue mentioned above.
>> 

-aneesh

  reply	other threads:[~2015-08-17 10:51 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-08-17  6:36 [RFC PATCH V1 0/8] KASAN ppc64 support Aneesh Kumar K.V
2015-08-17  6:36 ` [RFC PATCH V1 1/8] powerpc/mm: Add virt_to_pfn and use this instead of opencoding Aneesh Kumar K.V
2015-08-17  6:36 ` [RFC PATCH V1 2/8] kasan: MODULE_VADDR is not available on all archs Aneesh Kumar K.V
2015-08-17  6:36 ` [RFC PATCH V1 3/8] kasan: Rename kasan_enabled to kasan_report_enabled Aneesh Kumar K.V
2015-08-17  6:36 ` [RFC PATCH V1 4/8] kasan: Don't use kasan shadow pointer in generic functions Aneesh Kumar K.V
2015-08-17 11:36   ` Andrey Ryabinin
2015-08-18  5:29     ` Aneesh Kumar K.V
2015-08-18  9:12       ` Andrey Ryabinin
2015-08-17  6:36 ` [RFC PATCH V1 5/8] kasan: Enable arch to hook into kasan callbacks Aneesh Kumar K.V
2015-08-17  6:36 ` [RFC PATCH V1 6/8] kasan: Allow arch to overrride kasan shadow offsets Aneesh Kumar K.V
2015-08-17  6:36 ` [RFC PATCH V1 7/8] powerpc/mm: kasan: Add kasan support for ppc64 Aneesh Kumar K.V
2015-08-17 12:13   ` Andrey Ryabinin
2015-08-17 12:17     ` Andrey Ryabinin
2015-08-18  5:36       ` Aneesh Kumar K.V
2015-08-18  8:40         ` Andrey Ryabinin
2015-08-18  5:34     ` Aneesh Kumar K.V
2015-08-17  6:36 ` [RFC PATCH V1 8/8] powerpc: Disable kasan for kernel/ and mm/ directory Aneesh Kumar K.V
2015-08-17  6:54 ` [RFC PATCH V1 0/8] KASAN ppc64 support Benjamin Herrenschmidt
2015-08-17  9:50   ` Aneesh Kumar K.V
2015-08-17 10:01     ` Benjamin Herrenschmidt
2015-08-17 10:50       ` Aneesh Kumar K.V [this message]
2015-08-17 11:21         ` Benjamin Herrenschmidt
2015-08-17 11:29     ` Andrey Ryabinin
2015-08-18  5:42       ` Aneesh Kumar K.V
2015-08-18  8:50         ` Andrey Ryabinin
2015-08-18  9:21           ` Aneesh Kumar K.V
2015-08-18  9:30             ` Andrey Ryabinin

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87io8ep4sj.fsf@linux.vnet.ibm.com \
    --to=aneesh.kumar@linux.vnet.ibm.com \
    --cc=benh@kernel.crashing.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=mpe@ellerman.id.au \
    --cc=paulus@samba.org \
    --cc=ryabinin.a.a@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).