linux-kernel - [PATCH v4 0/8] KVM: Various fixes and improvements around kicking vCPUs

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Date:   Fri, 27 Aug 2021 11:25:08 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Eduardo Habkost <ehabkost@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 0/8] KVM: Various fixes and improvements around kicking vCPUs

Changes since v3:
- "KVM: x86: hyper-v: Avoid calling kvm_make_vcpus_request_mask() with
  vcpu_mask==NULL" patch added.
- Untangle kvm_make_all_cpus_request_except()/kvm_make_vcpus_request_mask()
 [Sean]
- "KVM: Drop 'except' parameter from kvm_make_vcpus_request_mask()" patch
 added [Sean]
- "KVM: Pre-allocate cpumasks for kvm_make_all_cpus_request_except()" patch
 added.
- "KVM: Make kvm_make_vcpus_request_mask() use pre-allocated cpu_kick_mask"
 patch added.
- Add Sean's R-b tag to PATCH6.

This series is a continuation to Sean's "[PATCH 0/2] VM: Fix a benign race
in kicking vCPUs" work and v2 for my "KVM: Optimize
kvm_make_vcpus_request_mask() a bit"/"KVM: x86: Fix stack-out-of-bounds
memory access from ioapic_write_indirect()" patchset.

>From Sean:

"Fix benign races when kicking vCPUs where the task doing the kicking can
consume a stale vcpu->cpu.  The races are benign because of the
impliciations of task migration with respect to interrupts and being in
guest mode, but IMO they're worth fixing if only as an excuse to
document the flows.

Patch 2 is a tangentially related cleanup to prevent future me from
trying to get rid of the NULL check on the cpumask parameters, which
_looks_ like it can't ever be NULL, but has a subtle edge case due to the
way CONFIG_CPUMASK_OFFSTACK=y handles cpumasks."

Patch3 is a preparation to untangling kvm_make_all_cpus_request_except()
and kvm_make_vcpus_request_mask().

Patch4 is a minor optimization for kvm_make_vcpus_request_mask() for big
guests.

Patch5 is a minor cleanup.

Patch6 fixes a real problem with ioapic_write_indirect() KVM does
out-of-bounds access to stack memory.

Patches7 and 8 get rid of dynamic cpumask allocation for kicking vCPUs.

Sean Christopherson (2):
  KVM: Clean up benign vcpu->cpu data races when kicking vCPUs
  KVM: KVM: Use cpumask_available() to check for NULL cpumask when
    kicking vCPUs

Vitaly Kuznetsov (6):
  KVM: x86: hyper-v: Avoid calling kvm_make_vcpus_request_mask() with
    vcpu_mask==NULL
  KVM: Optimize kvm_make_vcpus_request_mask() a bit
  KVM: Drop 'except' parameter from kvm_make_vcpus_request_mask()
  KVM: x86: Fix stack-out-of-bounds memory access from
    ioapic_write_indirect()
  KVM: Pre-allocate cpumasks for kvm_make_all_cpus_request_except()
  KVM: Make kvm_make_vcpus_request_mask() use pre-allocated
    cpu_kick_mask

 arch/x86/include/asm/kvm_host.h |   1 -
 arch/x86/kvm/hyperv.c           |  18 ++---
 arch/x86/kvm/ioapic.c           |  10 +--
 arch/x86/kvm/x86.c              |   8 +--
 include/linux/kvm_host.h        |   3 +-
 virt/kvm/kvm_main.c             | 118 ++++++++++++++++++++++++--------
 6 files changed, 106 insertions(+), 52 deletions(-)

-- 
2.31.1