From: "Egger, Christoph" <chegger@amazon.de>
To: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: hap_invlpg() vs INVLPGA
Date: Fri, 29 Jan 2016 15:02:38 +0100 [thread overview]
Message-ID: <56AB70FE.9030906@amazon.de> (raw)
In-Reply-To: <56AB6FB7.7030003@amazon.de>
On 29/01/16 14:57, Egger, Christoph wrote:
> On 29/01/16 14:24, Jan Beulich wrote:
>> Christoph,
>>
>> in commit dd6de3ab99 ("Implement Nested-on-Nested") you added
>> code to hap_invlpg() supposedly emulating INVLPGA. I've been
>> stumbling across this a number of times in the past, not being able
>> to make the connection between (a) VMX/EPT and INVLPGA and
>> (b) SVM's INVLPGA intercept and this function.
>
> When you boot Windows 7 as L1 guest and XP-Mode as L2 guest then
> L2 guest uses INVLPG instruction to invalidate a page and L1 guest
> handles this via using INVLPGA instruction.
>
> The INVLPG intercept flushes the nested hap p2m which is effectively
> a TLB flush to the L1 guest.
... actually to the L2 guest. Sorry for the typo.
> Then this intercept is injected into L1 guest.
>
> The INVLPGA instruction enforces a new ASID.
>
> If the nested hap p2m is NULL then p2m_flush() should effectively
> be a noop but it may not crash the guest.
>
> What I don't remember is if Windows 7 must be 32bit or 64bit
> to reproduce this.
>
> Christoph
>
>> I'm asking in the context of a reported crash resulting from the
>> nv_p2m field being NULL during emulation of an INVLPG instruction
>> in a guest with nesting enabled but - afaict - not actually used. Of
>> course I could submit a patch adding a NULL check here, but I'd
>> like to understand what this code is for, and hence whether the
>> better fix wouldn't be to get rid of it.
>>
>> Jan
>
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next prev parent reply other threads:[~2016-01-29 14:03 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-29 13:24 hap_invlpg() vs INVLPGA Jan Beulich
2016-01-29 13:57 ` Egger, Christoph
2016-01-29 14:02 ` Egger, Christoph [this message]
2016-01-29 15:53 ` Jan Beulich
2016-01-29 17:09 ` Egger, Christoph
2016-02-01 8:04 ` Jan Beulich
2016-02-01 8:14 ` Egger, Christoph
2016-02-01 9:00 ` Jan Beulich
2016-02-01 9:41 ` Egger, Christoph
2016-02-01 9:58 ` Jan Beulich
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