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From: Marc Zyngier <maz@kernel.org>
To: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	kvm@vger.kernel.org
Cc: James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Joey Gouly <joey.gouly@arm.com>,
	Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
	Xu Zhao <zhaoxu.35@bytedance.com>,
	Eric Auger <eric.auger@redhat.com>
Subject: [PATCH v2 11/11] KVM: arm64: Clarify the ordering requirements for vcpu/RD creation
Date: Wed, 20 Sep 2023 19:17:31 +0100	[thread overview]
Message-ID: <20230920181731.2232453-12-maz@kernel.org> (raw)
In-Reply-To: <20230920181731.2232453-1-maz@kernel.org>

It goes without saying, but it is probably better to spell it out:

If userspace tries to restore and VM, but creates vcpus and/or RDs
in a different order, the vcpu/RD mapping will be different. Yes,
our API is an ugly piece of crap and I can't believe that we missed
this.

If we want to relax the above, we'll need to define a new userspace
API that allows the mapping to be specified, rather than relying
on the kernel to perform the mapping on its own.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 Documentation/virt/kvm/devices/arm-vgic-v3.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/virt/kvm/devices/arm-vgic-v3.rst b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
index 51e5e5762571..5817edb4e046 100644
--- a/Documentation/virt/kvm/devices/arm-vgic-v3.rst
+++ b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
@@ -59,6 +59,13 @@ Groups:
   It is invalid to mix calls with KVM_VGIC_V3_ADDR_TYPE_REDIST and
   KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION attributes.
 
+  Note that to obtain reproducible results (the same VCPU being associated
+  with the same redistributor across a save/restore operation), VCPU creation
+  order, redistributor region creation order as well as the respective
+  interleaves of VCPU and region creation MUST be preserved.  Any change in
+  either ordering may result in a different vcpu_id/redistributor association,
+  resulting in a VM that will fail to run at restore time.
+
   Errors:
 
     =======  =============================================================
-- 
2.34.1


WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	kvm@vger.kernel.org
Cc: James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Joey Gouly <joey.gouly@arm.com>,
	Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
	Xu Zhao <zhaoxu.35@bytedance.com>,
	Eric Auger <eric.auger@redhat.com>
Subject: [PATCH v2 11/11] KVM: arm64: Clarify the ordering requirements for vcpu/RD creation
Date: Wed, 20 Sep 2023 19:17:31 +0100	[thread overview]
Message-ID: <20230920181731.2232453-12-maz@kernel.org> (raw)
In-Reply-To: <20230920181731.2232453-1-maz@kernel.org>

It goes without saying, but it is probably better to spell it out:

If userspace tries to restore and VM, but creates vcpus and/or RDs
in a different order, the vcpu/RD mapping will be different. Yes,
our API is an ugly piece of crap and I can't believe that we missed
this.

If we want to relax the above, we'll need to define a new userspace
API that allows the mapping to be specified, rather than relying
on the kernel to perform the mapping on its own.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 Documentation/virt/kvm/devices/arm-vgic-v3.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/virt/kvm/devices/arm-vgic-v3.rst b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
index 51e5e5762571..5817edb4e046 100644
--- a/Documentation/virt/kvm/devices/arm-vgic-v3.rst
+++ b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
@@ -59,6 +59,13 @@ Groups:
   It is invalid to mix calls with KVM_VGIC_V3_ADDR_TYPE_REDIST and
   KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION attributes.
 
+  Note that to obtain reproducible results (the same VCPU being associated
+  with the same redistributor across a save/restore operation), VCPU creation
+  order, redistributor region creation order as well as the respective
+  interleaves of VCPU and region creation MUST be preserved.  Any change in
+  either ordering may result in a different vcpu_id/redistributor association,
+  resulting in a VM that will fail to run at restore time.
+
   Errors:
 
     =======  =============================================================
-- 
2.34.1


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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2023-09-20 18:17 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-20 18:17 [PATCH v2 00/11] KVM: arm64: Accelerate lookup of vcpus by MPIDR values (and other fixes) Marc Zyngier
2023-09-20 18:17 ` Marc Zyngier
2023-09-20 18:17 ` [PATCH v2 01/11] KVM: arm64: vgic: Make kvm_vgic_inject_irq() take a vcpu pointer Marc Zyngier
2023-09-20 18:17   ` Marc Zyngier
2023-09-21  9:11   ` Zenghui Yu
2023-09-21  9:11     ` Zenghui Yu
2023-09-21 11:20     ` Marc Zyngier
2023-09-21 11:20       ` Marc Zyngier
2023-09-20 18:17 ` [PATCH v2 02/11] KVM: arm64: vgic-its: Treat the collection target address as a vcpu_id Marc Zyngier
2023-09-20 18:17   ` Marc Zyngier
2023-09-21  9:14   ` Zenghui Yu
2023-09-21  9:14     ` Zenghui Yu
2023-09-21 11:46     ` Marc Zyngier
2023-09-21 11:46       ` Marc Zyngier
2023-09-21 13:12       ` Zenghui Yu
2023-09-21 13:12         ` Zenghui Yu
2023-09-20 18:17 ` [PATCH v2 03/11] KVM: arm64: vgic-v3: Refactor GICv3 SGI generation Marc Zyngier
2023-09-20 18:17   ` Marc Zyngier
2023-09-21  9:42   ` Joey Gouly
2023-09-21  9:42     ` Joey Gouly
2023-09-21 11:13     ` Marc Zyngier
2023-09-21 11:13       ` Marc Zyngier
2023-09-20 18:17 ` [PATCH v2 04/11] KVM: arm64: vgic-v2: Use cpuid from userspace as vcpu_id Marc Zyngier
2023-09-20 18:17   ` Marc Zyngier
2023-09-20 18:17 ` [PATCH v2 05/11] KVM: arm64: vgic: Use vcpu_idx for the debug information Marc Zyngier
2023-09-20 18:17   ` Marc Zyngier
2023-09-20 18:17 ` [PATCH v2 06/11] KVM: arm64: Use vcpu_idx for invalidation tracking Marc Zyngier
2023-09-20 18:17   ` Marc Zyngier
2023-09-21  9:16   ` Zenghui Yu
2023-09-21  9:16     ` Zenghui Yu
2023-09-21 12:58     ` Marc Zyngier
2023-09-21 12:58       ` Marc Zyngier
2023-09-20 18:17 ` [PATCH v2 07/11] KVM: arm64: Simplify kvm_vcpu_get_mpidr_aff() Marc Zyngier
2023-09-20 18:17   ` Marc Zyngier
2023-09-20 18:17 ` [PATCH v2 08/11] KVM: arm64: Build MPIDR to vcpu index cache at runtime Marc Zyngier
2023-09-20 18:17   ` Marc Zyngier
2023-09-20 18:17 ` [PATCH v2 09/11] KVM: arm64: Fast-track kvm_mpidr_to_vcpu() when mpidr_data is available Marc Zyngier
2023-09-20 18:17   ` Marc Zyngier
2023-09-20 18:17 ` [PATCH v2 10/11] KVM: arm64: vgic-v3: Optimize affinity-based SGI injection Marc Zyngier
2023-09-20 18:17   ` Marc Zyngier
2023-09-21  9:32   ` Zenghui Yu
2023-09-21  9:32     ` Zenghui Yu
2023-09-20 18:17 ` Marc Zyngier [this message]
2023-09-20 18:17   ` [PATCH v2 11/11] KVM: arm64: Clarify the ordering requirements for vcpu/RD creation Marc Zyngier
2023-09-21  2:11 ` [PATCH v2 00/11] KVM: arm64: Accelerate lookup of vcpus by MPIDR values (and other fixes) Oliver Upton
2023-09-21  2:11   ` Oliver Upton
2023-09-21  9:39 ` Zenghui Yu
2023-09-21  9:39   ` Zenghui Yu

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