From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Kevin Tian <kevin.tian@intel.com>, Wei Liu <wei.liu2@citrix.com>,
GeorgeDunlap <george.dunlap@eu.citrix.com>,
Tim Deegan <tim@xen.org>, Xen-devel <xen-devel@lists.xen.org>,
Jun Nakajima <jun.nakajima@intel.com>
Subject: Re: [PATCH for-4.7] xen/nested_p2m: Don't walk EPT tables with a regular PT walker
Date: Fri, 13 May 2016 09:19:20 -0600 [thread overview]
Message-ID: <57360C9802000078000EB4A8@prv-mh.provo.novell.com> (raw)
In-Reply-To: <5735EC15.8080906@citrix.com>
>>> On 13.05.16 at 17:00, <andrew.cooper3@citrix.com> wrote:
> On 13/05/16 15:13, Jan Beulich wrote:
>>>>> On 13.05.16 at 15:33, <andrew.cooper3@citrix.com> wrote:
>>> + unsigned int l1_page_order;
>>> + int rv;
>>>
>>> /* translate l2 guest va into l2 guest gfn */
>>> p2m = p2m_get_nestedp2m(v, np2m_base);
>>> mode = paging_get_nestedmode(v);
>>> - gfn = mode->gva_to_gfn(v, p2m, va, pfec);
>>> + l2_gfn = mode->gva_to_gfn(v, p2m, va, pfec);
>>> +
>>> + if ( l2_gfn == INVALID_GFN )
>>> + return INVALID_GFN;
>>>
>>> /* translate l2 guest gfn into l1 guest gfn */
>>> - return hostmode->p2m_ga_to_gfn(v, hostp2m, np2m_base,
>>> - gfn << PAGE_SHIFT, &pfec_21, NULL);
>>> + rv = nestedhap_walk_L1_p2m(v, l2_gfn, &l1_gfn, &l1_page_order, &l1_p2ma,
>>> + 1,
>>> + !!(*pfec & PFEC_write_access),
>>> + !!(*pfec & PFEC_insn_fetch));
>>> +
>>> + return rv == NESTEDHVM_PAGEFAULT_DONE ? l1_gfn : INVALID_GFN;
>>> }
>> I'm really happy to see this getting cleaned up - I've stumbled across
>> the apparent brokenness here more than once, without ever finding
>> the time to help the situation. One question though: Is the return
>> value here correct even for l1_page_order > 0?
>
> Not completely sure. This code is messy, and my current testing is "it
> now doesn't crash where it used to crash before".
>
> The specific path being tripped over was __hvm_copy() performing an
> instruction fetch for emulation from the L2 guest.
>
> Looking at the code, if your caller only cares about 4K mappings, you
> will get the correct translation, due to the adjustment
> nept_walk_tables() makes.
Ah, indeed. But very odd for it to be done there, the more that "all
callers" is exactly one afaics. In that case may I suggest adding an
assertion to check that the respective bits in L1 and L2 GFN match?
Jan
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next prev parent reply other threads:[~2016-05-13 15:19 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-13 13:33 [PATCH for-4.7] xen/nested_p2m: Don't walk EPT tables with a regular PT walker Andrew Cooper
2016-05-13 14:13 ` Jan Beulich
2016-05-13 15:00 ` Andrew Cooper
2016-05-13 15:19 ` Jan Beulich [this message]
2016-05-13 17:25 ` [PATCH v2 " Andrew Cooper
2016-05-17 6:06 ` Tian, Kevin
2016-05-18 13:36 ` George Dunlap
2016-05-18 13:50 ` Wei Liu
2016-05-13 15:24 ` [PATCH " Andrew Cooper
2016-05-13 15:31 ` Jan Beulich
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