Hi George:
Beside the p2m_is_shared() need in p2m_pod_zero_check(),
In mem_sharing_nominate_page() line 524, there is a page type check,
and line 566, page handle is set.
So it looks like exists a competition on page type, mem_sharing_nominate_page()
may first find page is sharable and POD at same time put the page into it cache,
and later mem_sharing_nominate_page() set page handle, thus damage the page list
so we need to put mem_sharing_nominate_page into p2m_lock protect, right?
491int mem_sharing_nominate_page(struct p2m_domain *p2m,
492 unsigned long gfn,
493 int expected_refcnt,
494 shr_handle_t *phandle)
495{
496 p2m_type_t p2mt;
497 mfn_t mfn;
498 struct page_info *page;
499 int ret;
500 shr_handle_t handle;
501 shr_hash_entry_t *hash_entry;
502 struct gfn_info *gfn_info;
503 struct domain *d = p2m->domain;
504
505 *phandle = 0UL;
506
507 shr_lock();
508 mfn = gfn_to_mfn(p2m, gfn, &p2mt);
509
510 /* Check if mfn is valid */
511 ret = -EINVAL;
512 if (!mfn_valid(mfn))
513 goto out;
514
515 /* Return the handle if the page is already shared */
516 page = mfn_to_page(mfn);
517 if (p2m_is_shared(p2mt)) {
518 *phandle = page->shr_handle;
519 ret = 0;
520 goto out;
521 }
522
523 /* Check p2m type */
524 if (!p2m_is_sharable(p2mt))
525 goto out;
526
527 /* Try to convert the mfn to the sharable type */
528 ret = page_make_sharable(d, page, expected_refcnt);
529 if(ret)
530 goto out;
531
532 /* Create the handle */
533 ret = -ENOMEM;
534 handle = next_handle++;
535 if((hash_entry = mem_sharing_hash_insert(handle, mfn)) == NULL)
536 {
537 goto out;
538 }
539 if((gfn_info = mem_sharing_gfn_alloc()) == NULL)
540 {
541 mem_sharing_hash_destroy(hash_entry);
542 goto out;
543 }
544
545 /* Change the p2m type */
546 if(p2m_change_type(p2m, gfn, p2mt, p2m_ram_shared) != p2mt)
547 {
548 /* This is unlikely, as the type must have changed since we've checked
549 * it a few lines above.
550 * The mfn needs to revert back to rw type. This should never fail,
551 * since no-one knew that the mfn was temporarily sharable */
552 BUG_ON(page_make_private(d, page) != 0);
553 mem_sharing_hash_destroy(hash_entry);
554 mem_sharing_gfn_destroy(gfn_info, 0);
555 goto out;
556 }
557
558 /* Update m2p entry to SHARED_M2P_ENTRY */
559 set_gpfn_from_mfn(mfn_x(mfn), SHARED_M2P_ENTRY);
560
561 INIT_LIST_HEAD(&hash_entry->gfns);
562 INIT_LIST_HEAD(&gfn_info->list);
563 list_add(&gfn_info->list, &hash_entry->gfns);
564 gfn_info->gfn = gfn;
565 gfn_info->domain = d->domain_id;
566 page->shr_handle = handle;
567 *phandle = handle;
568
569 ret = 0;
570
571out:
572 shr_unlock();
573 return ret;
574}
> Date: Wed, 19 Jan 2011 09:11:37 +0000
> Subject: Re: [Xen-devel] RE: [PATCH] mem_sharing: fix race condition of nominate and unshare
> From: George.Dunlap@xxxxxxxxxxxxx
> To: tinnycloud@xxxxxxxxxxx
> CC: xen-devel@xxxxxxxxxxxxxxxxxxx; tim.deegan@xxxxxxxxxx; juihaochiang@xxxxxxxxx
>
> Very likely. If you look in xen/arch/x86/mm/p2m.c, the two functions
> which check a page to see if it can be reclaimed are
> "p2m_pod_zero_check*()". A little ways into each function there's a
> giant "if()" which has all of the conditions for reclaiming a page,
> starting with p2m_is_ram(). The easiest way to fix it is to add
> p2m_is_shared() to that "if" statement.
>
> -George
>
> 2011/1/19 MaoXiaoyun <tinnycloud@xxxxxxxxxxx>:
> > Hi George:
> >
> > I am working on the xen mem_sharing, I think the bug below is
> >
; related to POD.
> > (Test shows when POD is enable, it is easily hit the bug, when disabled, no
> > bug occurs).
> >
> > As I know when domU starts will POD, it gets memory from POD cache, and in
> > some
> > situation, POD cached will scan from Zero pages for reusing(link the page
> > into POD
> > cache page list), and from the page_info define, list and handle share same
> > posistion,
> > I think when reusing the page, POD doest't check page type, and if it is a
> > shared page
> > , it still can be put into POD cache, and thus handle is been overwritten.
> >
> > So maybe we need to check the page type before putting into cache,
> > What's your opinion?
> > thanks.
> >
> >>------------------------------------------------------------------
--------------
> >>From: tinnycloud@xxxxxxxxxxx
> >>To: juihaochiang@xxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxx
> >>CC: tim.deegan@xxxxxxxxxx
> >>Subject: RE: [PATCH] mem_sharing: fix race condition of nominate and
> >> unshare
> >>Date: Tue, 18 Jan 2011 20:05:16 +0800
> >>
> >>Hi:
> >>
> >> It is later found that caused by below patch code and I am using the
> >> blktap2.
> >>The handle retruned from here will later become ch in
> >> mem_sharing_share_pages, and then
> >>in mem_sharing_share_pages will have ch = sh, thus caused the problem.
> >>
> >>+ /* Return the handle if the page is already shared */
> >>+ page = mfn_to_page(mfn);
> >>+ if (p2m_is_shared(p2mt)) {
> >>+ &nbs
p; *phandle = page->shr_handle;
> >>+ ret = 0;
> >>+ goto out;
> >>+ }
> >>+
> >>
> >>But. after I removed the code, tests still failed, and this handle's value
> >> is not make sence.
> >>
> >>
> >>(XEN) ===>total handles 17834 total gfns 255853
> >>(XEN) handle 13856642536914634
> >>(XEN) Debug for domain=1, gfn=19fed, Debug page: MFN=349c0a is
> >> ci=8000000000000008, ti=8400000000000007, owner_id=32755
> >>(XEN) ----[ Xen-4.0.0 x86_64 debug=n Not tainted ]----
> >>(XEN) CPU: 15
> >>(XEN) RIP: e008:[<ffff82c4801bff4b>]
> >> mem_sharing_unshare_page+0x19b/0x720
> >>(XEN) RFLAGS:
0000000000010246 CONTEXT: hypervisor
> >>(XEN) rax: 0000000000000000 rbx: ffff83063fc67f28  ; rcx:
> >> 0000000000000092
> >>(XEN) rdx: 000000000000000a rsi: 000000000000000a rdi: ffff82c48021e9c4
> >>(XEN) rbp: ffff830440000000 rsp: ffff83063fc67c48 r8: 0000000000000001
> >>(XEN) r9: 0000000000000000 r10: 00000000fffffff8 r11: 0000000000000005
> >>(XEN) r12: 0000000000019fed r13: 0000000000000000 r14: 0000000000000000
> >>(XEN) r15: ffff82f606938140 cr0: 000000008005003b cr4: 00000000000026f0
> >>(XEN) cr3: 000000055513c000 cr2: 0000000000000018
> >>(XEN) ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: 0000 cs: e008
> >>(XEN)
Xen stack trace from rsp=ffff83063fc67c48:
> >>(XEN) 02c5f6c8b70fed66 39ef64058b487674 ffff82c4801a6082
> >> 0000000000000000
> >>(XEN) 00313a8b00313eca 0000000000000001 0000000000000009 ff
> >> ff830440000000
> >>(XEN) ffff83063fc67cb8 ffff82c4801df6f9 0000000000000040
> >> ffff83063fc67d04
> >>(XEN) 0000000000019fed 0000000d000001ed ffff83055458d000
> >> ffff83063fc67f28
> >>(XEN) 0000000000019fed 0000000000349c0a 0000000000000030
> >> ffff83063fc67f28
> >>(XEN) 0000000000000030 ffff82c48019baa6 ffff82c4802519c0
> >> 0000000d8016838e
> >>(XEN) 0000000000000000 00000000000001aa ffff8300bf554000
> >> ffff82c4801b3864
> >>(XEN) ffff830440000348 ffff8300bf5540
00 ffff8300bf5557f0
> >> ffff8300bf5557e8
> >>(XEN) 00000032027b81f2 ffff82c48026f080 ffff82c4801a9337
> >> ffff8300bf448000
> >>(XEN) ffff8300bf554000 ffff830000000000 0000000019fed000
> >> ffff8300bf2f2000
> >>(XEN) ffff82c48019985d 0000000000000080 ffff8300bf554000
> >> 0000000000019fed
> >>(XEN) ffff82c4801b08ba 000000000001e000 ffff82c48014931f ff
> >> ff8305570c6d50
> >>(XEN) ffff82c480251080 00000032027b81f2 ffff8305570c6d50
> >> ffff83052f3e2200
> >>(XEN) 0000000f027b7de0 ffff82c48011e07a 000000000000000f
> >> ffff82c48026f0a0
> >>(XEN) 0000000000000082 0000000000000000 0000000000000000
> >> 0000000000009e44
> >>(XEN) ffff8300bf554000 fff
f8300bf2f2000 ffff82c48011e07a
> >> 000000000000000f
> >>(XEN) ffff8300bf555760 0000000000000292 ffff82c48011afca
> >> 00000032028a8fc0
> >>(XEN) 0000000000000292 ffff82c4801a93c3 00000000000000ef
> >> ffff8300bf554000
> >>(XEN) ffff8300bf554000 ffff8300bf5557e8 ffff82c4801a6082
> >> ffff8300bf554000
> >>(XEN) 0000000000000000 ffff82c4801a0cc8 ffff8300bf554000
> >> ffff8300bf554000
> >>(XEN) Xen call trace:
> >>(XEN) [<ffff82c4801bff4b>] mem_sharing_unshare_page+0x19b/0x720
> >>(XEN) [<ffff82c4801a6082>] v lapic_has_pending_irq+0x42/0x70
> >>(XEN) [<ffff82c4801df6f9>] ept_get_entry+0xa9/0x1c0
> >>(XEN) [<ffff82c48019baa6>] hvm_hap_nested_page_fau
lt+0xd6/0x190
> >>(XEN) [<ffff82c4801b3864>] vmx_vmexit_handler+0x304/0x1a90
> >>(XEN) [<ffff82c4801a9337>] pt_restore_timer+0x57/0xb0
> >>(XEN) [<ffff82c48019985d>] hvm_do_resume+0x1d/0x130
> >>(XEN) [<ffff82c4801b08ba>] vmx_do_resume+0x11a/0x1c0
> >>(XEN) [<ffff82c48014931f>] context_switch+0x76f/0xf00
> >>(XEN) [<ffff82c48011e07a>] add_entry+0x3a/0xb0
> >>(XEN) [<ffff82c48011e07a>] add_entry+0x3a/0xb0
> >>(XEN) [<ffff82c48011afca>] schedule+0x1ea/0x500
> >>(XEN) [<ffff82c4801a93c3>] pt_update_irq+0x33/0x1e0
> >>(XEN) [< ;ffff82c4801a6082>] vlapic_has_pending_irq+0x42/0x70
> >>(XEN) [<
ffff82c4801a0cc8>] hvm_vcpu_has_pending_irq+0x88/0xa0
> >>(XEN) [<ffff82c4801b267b>] vmx_vmenter_helper+0x5b/0x150
> >>(XEN) [<ffff82c4801adaa3>] vmx_asm_do_vmentry+0x0/0xdd
> >>(XEN)
> >>(XEN) Pagetable walk from 0000000000000018:
> >>(XEN) L4[0x000] = 0000000000000000 ffffffffffffffff
> >>(XEN)
> >>(XEN) ****************************************
> >>(XEN) Panic on CPU 15:
> >>(XEN) FATAL PAGE FAULT
> >>(XEN) [error_code=0000]
> >>(XEN) Faulting linear address: 0000000000000018
> >>(XEN) ****************************************
> >>(XEN)
> >>(XEN) Manual reset required ('noreboot' specified)
> >>
> >>
> >>
> >>
> >>
> >> ----------------------------------------------------------------
-----------------------------------
> >>>From: tinnycloud@xxxxxxxxxxx
> >>>To: juihaochiang@xxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxx
> >>>CC: tim.deegan@xxxxxxxxxx
> >>>Subject: RE: [PATCH] mem_sharing: fix race condition of nominate and
> >>> unshare
> >>>Date: Tue, 18 Jan 2011 17:42:32 +0800
> >>
> >>>Hi Tim & Jui-Hao:
> >>
> >> > When I use Linux HVM instead of Windows HVM, more bug shows up.
> >>
> >>> I only start on VM, and when I destroy it , xen crashed on
> >>> mem_sharing_unshare_page()
> >>>which in line709, hash_entry is NULL. Later I found the handle has been
> >>> removed in
> >>>mem_sharing_share_pages(), please refer logs below.
> >>
> >
> > _____
__________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >
> >
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