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From: Nadav Amit <namit@vmware.com>
To: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [kvm-unit-tests PATCH] x86: svm: low CR3 bits are not MBZ
Date: Wed, 15 Jul 2020 22:27:30 +0000	[thread overview]
Message-ID: <9DC37B0B-597A-4B31-8397-B6E4764EEA37@vmware.com> (raw)
In-Reply-To: <fe76d847-5106-bc09-e4cf-498fb51e5255@oracle.com>

> On Jul 15, 2020, at 3:21 PM, Krish Sadhukhan <krish.sadhukhan@oracle.com> wrote:
> 
> 
> On 7/13/20 4:30 PM, Nadav Amit wrote:
>>> On Jul 13, 2020, at 4:17 PM, Krish Sadhukhan <krish.sadhukhan@oracle.com> wrote:
>>> 
>>> 

[snip]

>>> I am just saying that the APM language "should be cleared to 0" is misleading if the processor doesn't enforce it.
>> Just to ensure I am clear - I am not blaming you in any way. I also found
>> the phrasing confusing.
>> 
>> Having said that, if you (or anyone else) reintroduces “positive” tests, in
>> which the VM CR3 is modified to ensure VM-entry succeeds when the reserved
>> non-MBZ bits are set, please ensure the tests fails gracefully. The
>> non-long-mode CR3 tests crashed since the VM page-tables were incompatible
>> with the paging mode.
>> 
>> In other words, instead of setting a VMMCALL instruction in the VM to trap
>> immediately after entry, consider clearing the present-bits in the high
>> levels of the NPT; or injecting some exception that would trigger exit
>> during vectoring or something like that.
>> 
>> P.S.: If it wasn’t clear, I am not going to fix KVM itself for some obvious
>> reasons.
> I think since the APM is not clear, re-adding any test that tests those bits, is like adding a test with "undefined behavior" to me.
> 
> 
> Paolo, Should I send a KVM patch to remove checks for those non-MBZ reserved bits ?

Which non-MBZ reserved bits (other than those that I addressed) do you refer
to?


  reply	other threads:[~2020-07-15 22:27 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-13  4:39 [kvm-unit-tests PATCH] x86: svm: low CR3 bits are not MBZ Nadav Amit
2020-07-13 23:06 ` Krish Sadhukhan
2020-07-13 23:11   ` Nadav Amit
2020-07-13 23:17     ` Krish Sadhukhan
2020-07-13 23:30       ` Nadav Amit
2020-07-15 22:21         ` Krish Sadhukhan
2020-07-15 22:27           ` Nadav Amit [this message]
2020-07-15 22:39             ` Krish Sadhukhan
2020-07-15 22:51               ` Nadav Amit
2020-07-15 23:12               ` Jim Mattson
2020-08-04 23:13                 ` Krish Sadhukhan
2020-08-18  6:38                   ` Paolo Bonzini
2020-08-18 18:25                     ` Krish Sadhukhan
2020-08-29  1:39                       ` Krish Sadhukhan
2020-07-28 21:27           ` Paolo Bonzini
2020-07-28 21:27 ` Paolo Bonzini

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