[PATCH 0/7] KVM: Ensure WAIT requests actually wait
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From: Sean Christopherson <seanjc@google.com>
Date: 2026-10-28 19:03:02
Also in:
kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-mips, linux-riscv, lkml, loongarch
Subsystem:
kernel virtual machine (kvm), kernel virtual machine for powerpc (kvm/powerpc), kernel virtual machine for s390 (kvm/s390), linux for powerpc (32-bit and 64-bit), s390 architecture, the rest · Maintainers:
Paolo Bonzini, Madhavan Srinivasan, Christian Borntraeger, Janosch Frank, Claudio Imbrenda, Heiko Carstens, Vasily Gorbik, Alexander Gordeev, Linus Torvalds
Fix a bug in where kvm_make_request_and_kick() won't actually wait if the kick races without another non-waiting kick. The issue is that all of the conditional kvm_arch_vcpu_should_kick() implementations are missing this code: if (req & KVM_REQUEST_WAIT) return mode != OUTSIDE_GUEST_MODE; Thankfully, kvm_request_needs_ipi() does the right thing, so this doesn't affect kvm_make_all_cpus_request() or kvm_make_vcpus_request_mask(), i.e. it's limited to x86 SNP's used of kvm_make_request_and_kick(). To fix, address this TODO: /* TODO: merge with kvm_arch_vcpu_should_kick */ and purge kvm_arch_vcpu_should_kick(). As usual, PPC makes that difficult because it has wonky code that is poorly documented. For reasons unknown, kvm_vcpu_kick() unconditionally returns true on (most flavors of) PPC. To preserve that behavior, add a compatibility wrapper in PPC, along with a @force param to __kvm_vcpu_kick(). This series would ideally go into 7.4, even though it's obviously not small, as guest_memfd in-place conversion massively widens the window where a missed kick+wait can lead to the host trying to reclaim an in-use VMSA page, which is generally fatal to the host. Sean Christopherson (7): KVM: s390: Drop unused and unreachable kvm_arch_vcpu_should_kick() KVM: Add a @force param to __kvm_vcpu_kick() for PPC backwards compatibility KVM: PPC: Explicitly force IPIs when directly kicking vCPUs KVM: MIPS: Rework kvm_arch_vcpu_should_kick() to use standard implementation KVM: Move kvm_arch_vcpu_should_kick() to common code as kvm_vcpu_should_kick() KVM: Plumb the full request into __kvm_vcpu_kick() KVM: Drop kvm_vcpu_should_kick() and use kvm_request_needs_ipi() arch/arm64/kvm/arm.c | 5 ----- arch/loongarch/kvm/vcpu.c | 5 ----- arch/mips/kvm/mips.c | 5 ----- arch/powerpc/include/asm/kvm_ppc.h | 13 ++++++++++++- arch/powerpc/kvm/book3s.c | 4 ++-- arch/powerpc/kvm/book3s_pr.c | 2 +- arch/powerpc/kvm/booke.c | 6 +++--- arch/powerpc/kvm/e500_emulate.c | 2 +- arch/powerpc/kvm/powerpc.c | 7 +------ arch/riscv/kvm/vcpu.c | 5 ----- arch/s390/kvm/s390/s390.c | 7 ------- arch/x86/kvm/x86.c | 5 ----- include/linux/kvm_host.h | 7 +++---- virt/kvm/kvm_main.c | 28 ++++++++++++++++------------ 14 files changed, 39 insertions(+), 62 deletions(-) base-commit: 7e60162b16f9da0d2fa83da5c1723b6853a0ac1d -- 2.56.0.313.g2479322e68-goog