From: Gleb Natapov <gleb@redhat.com>
To: Xiao Guangrong <xiaoguangrong.eric@gmail.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>,
avi.kivity@gmail.com, mtosatti@redhat.com, pbonzini@redhat.com,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
aarcange@redhat.com
Subject: Re: [PATCH v3 10/15] KVM: MMU: allocate shadow pages from slab
Date: Thu, 24 Oct 2013 15:32:39 +0300 [thread overview]
Message-ID: <20131024123239.GA26465@redhat.com> (raw)
In-Reply-To: <5268FE1D.50809@gmail.com>
On Thu, Oct 24, 2013 at 07:01:49PM +0800, Xiao Guangrong wrote:
> On 10/24/2013 06:39 PM, Gleb Natapov wrote:
> > On Thu, Oct 24, 2013 at 06:10:46PM +0800, Xiao Guangrong wrote:
> >> On 10/24/2013 05:52 PM, Gleb Natapov wrote:
> >>> On Thu, Oct 24, 2013 at 05:29:44PM +0800, Xiao Guangrong wrote:
> >>>> On 10/24/2013 05:19 PM, Gleb Natapov wrote:
> >>>>
> >>>>>> @@ -946,7 +947,7 @@ static inline struct kvm_mmu_page *page_header(hpa_t shadow_page)
> >>>>>> {
> >>>>>> struct page *page = pfn_to_page(shadow_page >> PAGE_SHIFT);
> >>>>>>
> >>>>>> - return (struct kvm_mmu_page *)page_private(page);
> >>>>>> + return (struct kvm_mmu_page *)(page->mapping);
> >>>>> Why?
> >>>>
> >>>> That's because page->private has been used by slab:
> >>>>
> >>> But does lockless path actually looks at it?
> >>
> >> Lockless path does not use it, however, it is used by kvm_mmu_page():
> >>
> >> static inline struct kvm_mmu_page *page_header(hpa_t shadow_page)
> >> {
> >> struct page *page = pfn_to_page(shadow_page >> PAGE_SHIFT);
> >>
> >> return (struct kvm_mmu_page *)(page->mapping);
> >> }
> >>
> >> which is used in the common code.
> > Ah, so the pointer is not available even after object is allocated.
> > Make sense since we allocate object, not page here, but is it safe to
> > use mapping like that?
>
> The commens says:
>
> struct address_space *mapping; /* If low bit clear, points to
> * inode address_space, or NULL.
> * If page mapped as anonymous
> * memory, low bit is set, and
> * it points to anon_vma object:
> * see PAGE_MAPPING_ANON below.
>
> It seems mapping is used for address_space or anonymous memory, in
> our case, the page is used by slab, so I guess it is ok. And the bug
> i put in set_page_header() was not tiggered on both slab and slub.
>
Yeah, I also think so. I asked Andrea (copied) and he thinks that it is
safe too currently, but things changes fast in this area. Andrea?
Another option is too save slab_cache pointer and reset it before
freeing the object but it looks ugly.
--
Gleb.
next prev parent reply other threads:[~2013-10-24 12:32 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-23 13:29 [PATCH v3 00/15] KVM: MMU: locklessly write-protect Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 01/15] KVM: MMU: properly check last spte in fast_page_fault() Xiao Guangrong
2013-11-12 0:25 ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 02/15] KVM: MMU: lazily drop large spte Xiao Guangrong
2013-11-12 22:44 ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 03/15] KVM: MMU: flush tlb if the spte can be locklessly modified Xiao Guangrong
2013-11-13 0:10 ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 04/15] KVM: MMU: flush tlb out of mmu lock when write-protect the sptes Xiao Guangrong
2013-11-14 0:36 ` Marcelo Tosatti
2013-11-14 5:15 ` Xiao Guangrong
2013-11-14 18:39 ` Marcelo Tosatti
2013-11-15 7:09 ` Xiao Guangrong
2013-11-19 0:19 ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 05/15] KVM: MMU: update spte and add it into rmap before dirty log Xiao Guangrong
2013-11-15 0:08 ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 06/15] KVM: MMU: redesign the algorithm of pte_list Xiao Guangrong
2013-11-19 0:48 ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 07/15] KVM: MMU: introduce nulls desc Xiao Guangrong
2013-11-22 19:14 ` Marcelo Tosatti
2013-11-25 6:11 ` Xiao Guangrong
2013-11-25 6:29 ` Xiao Guangrong
2013-11-25 18:12 ` Marcelo Tosatti
2013-11-26 3:21 ` Xiao Guangrong
2013-11-26 10:12 ` Gleb Natapov
2013-11-26 19:31 ` Marcelo Tosatti
2013-11-28 8:53 ` Xiao Guangrong
2013-12-03 7:10 ` Xiao Guangrong
2013-12-05 13:50 ` Marcelo Tosatti
2013-12-05 15:30 ` Xiao Guangrong
2013-12-06 0:15 ` Marcelo Tosatti
2013-12-06 0:22 ` Marcelo Tosatti
2013-12-10 6:58 ` Xiao Guangrong
2013-11-25 10:19 ` Gleb Natapov
2013-11-25 10:25 ` Xiao Guangrong
2013-11-25 12:48 ` Avi Kivity
2013-11-25 14:23 ` Marcelo Tosatti
2013-11-25 14:29 ` Gleb Natapov
2013-11-25 18:06 ` Marcelo Tosatti
2013-11-26 3:10 ` Xiao Guangrong
2013-11-26 10:15 ` Gleb Natapov
2013-11-26 19:58 ` Marcelo Tosatti
2013-11-28 8:32 ` Xiao Guangrong
2013-11-25 14:08 ` Marcelo Tosatti
2013-11-26 3:02 ` Xiao Guangrong
2013-11-25 9:31 ` Peter Zijlstra
2013-11-25 10:59 ` Xiao Guangrong
2013-11-25 11:05 ` Peter Zijlstra
2013-11-25 11:29 ` Peter Zijlstra
2013-10-23 13:29 ` [PATCH v3 08/15] KVM: MMU: introduce pte-list lockless walker Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 09/15] KVM: MMU: initialize the pointers in pte_list_desc properly Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 10/15] KVM: MMU: allocate shadow pages from slab Xiao Guangrong
2013-10-24 9:19 ` Gleb Natapov
2013-10-24 9:29 ` Xiao Guangrong
2013-10-24 9:52 ` Gleb Natapov
2013-10-24 10:10 ` Xiao Guangrong
2013-10-24 10:39 ` Gleb Natapov
2013-10-24 11:01 ` Xiao Guangrong
2013-10-24 12:32 ` Gleb Natapov [this message]
2013-10-28 3:16 ` Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 11/15] KVM: MMU: locklessly access shadow page under rcu protection Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 12/15] KVM: MMU: check last spte with unawareness of mapping level Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 13/15] KVM: MMU: locklessly write-protect the page Xiao Guangrong
2013-10-24 9:17 ` Gleb Natapov
2013-10-24 9:24 ` Xiao Guangrong
2013-10-24 9:32 ` Gleb Natapov
2013-10-23 13:29 ` [PATCH v3 14/15] KVM: MMU: clean up spte_write_protect Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 15/15] KVM: MMU: use rcu functions to access the pointer Xiao Guangrong
2013-11-03 12:29 ` [PATCH v3 00/15] KVM: MMU: locklessly write-protect Gleb Natapov
2013-11-11 5:33 ` Xiao Guangrong
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=20131024123239.GA26465@redhat.com \
--to=gleb@redhat.com \
--cc=aarcange@redhat.com \
--cc=avi.kivity@gmail.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mtosatti@redhat.com \
--cc=pbonzini@redhat.com \
--cc=xiaoguangrong.eric@gmail.com \
--cc=xiaoguangrong@linux.vnet.ibm.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).