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From: Sean Christopherson <seanjc@google.com>
To: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Cc: kvm@vger.kernel.org, pbonzini@redhat.com, jmattson@google.com
Subject: Re: [PATCH 3/7 v7] KVM: nSVM: No need to set bits 11:0 in MSRPM and IOPM bitmaps
Date: Fri, 23 Apr 2021 15:56:22 +0000
Message-ID: <YILuJohrTE+P06tt@google.com> (raw)
In-Reply-To: <a9f74546-6ab7-88fc-83d1-382b380f6264@oracle.com>

On Thu, Apr 22, 2021, Krish Sadhukhan wrote:
> On 4/22/21 11:01 AM, Sean Christopherson wrote:
> > 		offset = svm->nested.ctl.msrpm_base_pa + (p * 4);
> > 
> > 		if (kvm_vcpu_read_guest(&svm->vcpu, offset, &value, 4)) <- This reads vmcb12
> > 			return false;
> > 
> > 		svm->nested.msrpm[p] = svm->msrpm[p] | value; <- Merge vmcb12's bitmap to KVM's bitmap for L2

... 
 
> Getting back to your concern that this patch breaks
> nested_svm_vmrun_msrpm().  If L1 passes a valid address in which some bits
> in 11:0 are set, the hardware is anyway going to ignore those bits,
> irrespective of whether we clear them (before my patch) or pass them as is
> (my patch) and therefore what L1 thinks as a valid address will effectively
> be an invalid address to the hardware. The only difference my patch makes is
> it enables tests to verify hardware behavior. Am missing something ?

See the above snippet where KVM reads the effectively vmcb12->msrpm to merge L1's
desires with KVM's desires.  By removing the code that ensures
svm->nested.ctl.msrpm_base_pa is page aligned, the above offset calculation will
be wrong.

  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-12 21:56 [PATCH 0/7 v7] KVM: nSVM: Check addresses of MSR bitmap and IO bitmap tables on vmrun of nested guests Krish Sadhukhan
2021-04-12 21:56 ` [PATCH 1/7 v7] KVM: SVM: Define actual size of IOPM and MSRPM tables Krish Sadhukhan
2021-04-12 21:56 ` [PATCH 2/7 v7] KVM: nSVM: Define an exit code to reflect consistency check failure Krish Sadhukhan
2021-04-17 14:17   ` Paolo Bonzini
2021-04-19 17:57     ` Krish Sadhukhan
2021-04-19 18:28       ` Paolo Bonzini
2021-04-19 18:36         ` Jim Mattson
2021-04-12 21:56 ` [PATCH 3/7 v7] KVM: nSVM: No need to set bits 11:0 in MSRPM and IOPM bitmaps Krish Sadhukhan
2021-04-17 14:18   ` Paolo Bonzini
2021-04-20 20:00   ` Sean Christopherson
2021-04-22 17:50     ` Krish Sadhukhan
2021-04-22 17:52       ` Krish Sadhukhan
2021-04-22 17:56       ` Krish Sadhukhan
2021-04-22 18:01         ` Sean Christopherson
2021-04-23  1:12           ` Krish Sadhukhan
2021-04-23 15:56             ` Sean Christopherson [this message]
2021-04-23 20:31               ` Paolo Bonzini
2021-04-26 21:59                 ` Krish Sadhukhan
2021-04-26 22:07                   ` Sean Christopherson
2021-04-12 21:56 ` [PATCH 4/7 v7] nSVM: Check addresses of MSR and IO permission maps Krish Sadhukhan
2021-04-12 21:56 ` [PATCH 5/7 v7] SVM: Use ALIGN macro when aligning 'io_bitmap_area' Krish Sadhukhan
2021-04-12 21:56 ` [PATCH 6/7 v7] nSVM: Define an exit code to reflect consistency check failure Krish Sadhukhan
2021-04-12 21:56 ` [PATCH 7/7 v7] nSVM: Test addresses of MSR and IO permissions maps Krish Sadhukhan
2021-04-17 14:35 ` [PATCH 0/7 v7] KVM: nSVM: Check addresses of MSR bitmap and IO bitmap tables on vmrun of nested guests Paolo Bonzini

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