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From: Maxim Levitsky <mlevitsk@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Li RongQing <lirongqing@baidu.com>
Subject: Re: [PATCH 03/19] Revert "KVM: SVM: Introduce hybrid-AVIC mode"
Date: Wed, 31 Aug 2022 20:47:53 +0300	[thread overview]
Message-ID: <d12df38c5b4ee493e63771000cbc4b723b4defe1.camel@redhat.com> (raw)
In-Reply-To: <Yw+KDoSSKN0xgJW0@google.com>

On Wed, 2022-08-31 at 16:19 +0000, Sean Christopherson wrote:
> On Wed, Aug 31, 2022, Maxim Levitsky wrote:
> > On Wed, 2022-08-31 at 00:34 +0000, Sean Christopherson wrote:
> > > Remove SVM's so called "hybrid-AVIC mode" and reinstate the restriction
> > > where AVIC is disabled if x2APIC is enabled.  The argument that the
> > > "guest is not supposed to access xAPIC mmio when uses x2APIC" is flat out
> > > wrong.  Activating x2APIC completely disables the xAPIC MMIO region,
> > > there is nothing that says the guest must not access that address.
> > > 
> > > Concretely, KVM-Unit-Test's existing "apic" test fails the subtests that
> > > expect accesses to the APIC base region to not be emulated when x2APIC is
> > > enabled.
> > > 
> > > Furthermore, allowing the guest to trigger MMIO emulation in a mode where
> > > KVM doesn't expect such emulation to occur is all kinds of dangerous.
> > > 
> > > Tweak the restriction so that it only inhibits AVIC if x2APIC is actually
> > > enabled instead of inhibiting AVIC is x2APIC is exposed to the guest.
> > > 
> > > This reverts commit 0e311d33bfbef86da130674e8528cc23e6acfe16.
> > 
> > I don't agree with this patch.
> > 
> > When reviewing this code I did note that MMIO is left enabled which is kind
> > of errata on KVM side, and nobody objected to this.
> 
> I didn't object because I didn't read the patch.  I'm very much objecting now.
> 

And I am *very* much objecting to reverting this patch.

Best regards,
	Maxim Levitsky


  reply	other threads:[~2022-08-31 17:48 UTC|newest]

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-31  0:34 [PATCH 00/19] KVM: x86: AVIC and local APIC fixes+cleanups Sean Christopherson
2022-08-31  0:34 ` [PATCH 01/19] KVM: SVM: Process ICR on AVIC IPI delivery failure due to invalid target Sean Christopherson
2022-08-31  9:18   ` Maxim Levitsky
2022-08-31  0:34 ` [PATCH 02/19] KVM: SVM: Don't put/load AVIC when setting virtual APIC mode Sean Christopherson
2022-08-31  9:24   ` Maxim Levitsky
2022-08-31 16:33     ` Sean Christopherson
2022-08-31  0:34 ` [PATCH 03/19] Revert "KVM: SVM: Introduce hybrid-AVIC mode" Sean Christopherson
2022-08-31  5:59   ` Maxim Levitsky
2022-08-31  6:45     ` Maxim Levitsky
2022-08-31 16:29       ` Sean Christopherson
2022-08-31 17:46         ` Maxim Levitsky
2022-08-31 17:58           ` Jim Mattson
2022-08-31 18:01             ` Maxim Levitsky
2022-08-31 19:12           ` Sean Christopherson
2022-09-01 10:25             ` Maxim Levitsky
2022-09-01 11:47               ` Jim Mattson
2022-09-01 13:29               ` Sean Christopherson
2022-09-01 13:53               ` Sean Christopherson
2022-09-01 15:08               ` Sean Christopherson
2022-08-31 16:19     ` Sean Christopherson
2022-08-31 17:47       ` Maxim Levitsky [this message]
2022-08-31  0:34 ` [PATCH 04/19] KVM: SVM: Replace "avic_mode" enum with "x2avic_enabled" boolean Sean Christopherson
2022-08-31  9:36   ` Maxim Levitsky
2022-08-31  0:34 ` [PATCH 05/19] KVM: SVM: Compute dest based on sender's x2APIC status for AVIC kick Sean Christopherson
2022-08-31  9:38   ` Maxim Levitsky
2022-09-01  2:56   ` Li,Rongqing
2022-08-31  0:34 ` [PATCH 06/19] KVM: SVM: Get x2APIC logical dest bitmap from ICRH[15:0], not ICHR[31:16] Sean Christopherson
2022-08-31  6:09   ` Maxim Levitsky
2022-08-31  9:43     ` Maxim Levitsky
2022-08-31 16:35       ` Sean Christopherson
2022-08-31 18:18         ` Maxim Levitsky
2022-08-31  0:34 ` [PATCH 07/19] KVM: SVM: Drop buggy and redundant AVIC "single logical dest" check Sean Christopherson
2022-08-31  6:19   ` Maxim Levitsky
2022-08-31 16:37     ` Sean Christopherson
2022-08-31 18:10       ` Maxim Levitsky
2022-08-31  0:34 ` [PATCH 08/19] KVM: SVM: Remove redundant cluster calculation that also creates a shadow Sean Christopherson
2022-08-31 10:19   ` Maxim Levitsky
2022-09-01 20:02     ` Sean Christopherson
2022-08-31  0:34 ` [PATCH 09/19] KVM: SVM: Drop duplicate calcuation of AVIC/x2AVIC "logical index" Sean Christopherson
2022-08-31  0:34 ` [PATCH 10/19] KVM: SVM: Document that vCPU ID == APIC ID in AVIC kick fastpatch Sean Christopherson
2022-08-31 10:22   ` Maxim Levitsky
2022-08-31 16:16     ` Sean Christopherson
2022-08-31 17:49       ` Maxim Levitsky
2022-08-31  0:34 ` [PATCH 11/19] KVM: SVM: Add helper to perform final AVIC "kick" of single vCPU Sean Christopherson
2022-08-31 10:25   ` Maxim Levitsky
2022-08-31 15:08     ` Sean Christopherson
2022-08-31 18:12       ` Maxim Levitsky
2022-08-31  0:34 ` [PATCH 12/19] KVM: x86: Disable APIC logical map if logical ID covers multiple MDAs Sean Christopherson
2022-08-31 13:23   ` Maxim Levitsky
2022-08-31  0:35 ` [PATCH 13/19] KVM: x86: Disable APIC logical map if vCPUs are aliased in logical mode Sean Christopherson
2022-08-31 13:24   ` Maxim Levitsky
2022-08-31  0:35 ` [PATCH 14/19] KVM: x86: Honor architectural behavior for aliased 8-bit APIC IDs Sean Christopherson
2022-08-31 13:37   ` Maxim Levitsky
2022-08-31 16:41     ` Sean Christopherson
2022-08-31 17:51       ` Maxim Levitsky
2022-08-31  0:35 ` [PATCH 15/19] KVM: x86: Explicitly skip optimized logical map setup if vCPU's LDR==0 Sean Christopherson
2022-08-31 13:41   ` Maxim Levitsky
2022-08-31 16:47     ` Sean Christopherson
2022-08-31  0:35 ` [PATCH 16/19] KVM: x86: Explicitly track all possibilities for APIC map's logical modes Sean Christopherson
2022-08-31 13:43   ` Maxim Levitsky
2022-08-31 16:56     ` Sean Christopherson
2022-08-31 17:53       ` Maxim Levitsky
2022-09-16 18:58         ` Sean Christopherson
2022-08-31 18:42   ` Maxim Levitsky
2022-08-31 19:17     ` Sean Christopherson
2022-08-31  0:35 ` [PATCH 17/19] KVM: SVM: Handle multiple logical targets in AVIC kick fastpath Sean Christopherson
2022-08-31 13:57   ` Maxim Levitsky
2022-08-31 18:19     ` Sean Christopherson
2022-08-31 18:25       ` Maxim Levitsky
2022-08-31  0:35 ` [PATCH 18/19] KVM: SVM: Ignore writes to Remote Read Data on AVIC write traps Sean Christopherson
2022-08-31 10:40   ` Maxim Levitsky
2022-08-31  0:35 ` [PATCH 19/19] Revert "KVM: SVM: Do not throw warning when calling avic_vcpu_load on a running vcpu" Sean Christopherson
2022-08-31  6:07   ` Maxim Levitsky
2022-08-31  7:03     ` Maxim Levitsky

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