This is a note to let you know that I've just added the patch titled KVM: x86: Wait for IPIs to be delivered when handling Hyper-V TLB flush hypercall to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-x86-wait-for-ipis-to-be-delivered-when-handling-hyper-v-tlb-flush-hypercall.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 1ebfaa11ebb5b603a3c3f54b2e84fcf1030f5a14 Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Date: Thu, 9 Dec 2021 11:29:37 +0100 Subject: KVM: x86: Wait for IPIs to be delivered when handling Hyper-V TLB flush hypercall From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> commit 1ebfaa11ebb5b603a3c3f54b2e84fcf1030f5a14 upstream. Prior to commit 0baedd792713 ("KVM: x86: make Hyper-V PV TLB flush use tlb_flush_guest()"), kvm_hv_flush_tlb() was using 'KVM_REQ_TLB_FLUSH | KVM_REQUEST_NO_WAKEUP' when making a request to flush TLBs on other vCPUs and KVM_REQ_TLB_FLUSH is/was defined as: (0 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP) so KVM_REQUEST_WAIT was lost. Hyper-V TLFS, however, requires that "This call guarantees that by the time control returns back to the caller, the observable effects of all flushes on the specified virtual processors have occurred." and without KVM_REQUEST_WAIT there's a small chance that the vCPU making the TLB flush will resume running before all IPIs get delivered to other vCPUs and a stale mapping can get read there. Fix the issue by adding KVM_REQUEST_WAIT flag to KVM_REQ_TLB_FLUSH_GUEST: kvm_hv_flush_tlb() is the sole caller which uses it for kvm_make_all_cpus_request()/kvm_make_vcpus_request_mask() where KVM_REQUEST_WAIT makes a difference. Cc: stable@xxxxxxxxxx Fixes: 0baedd792713 ("KVM: x86: make Hyper-V PV TLB flush use tlb_flush_guest()") Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Message-Id: <20211209102937.584397-1-vkuznets@xxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/include/asm/kvm_host.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -85,7 +85,7 @@ KVM_ARCH_REQ_FLAGS(25, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP) #define KVM_REQ_TLB_FLUSH_CURRENT KVM_ARCH_REQ(26) #define KVM_REQ_TLB_FLUSH_GUEST \ - KVM_ARCH_REQ_FLAGS(27, KVM_REQUEST_NO_WAKEUP) + KVM_ARCH_REQ_FLAGS(27, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP) #define KVM_REQ_APF_READY KVM_ARCH_REQ(28) #define KVM_REQ_MSR_FILTER_CHANGED KVM_ARCH_REQ(29) Patches currently in stable-queue which might be from vkuznets@xxxxxxxxxx are queue-5.10/kvm-x86-wait-for-ipis-to-be-delivered-when-handling-hyper-v-tlb-flush-hypercall.patch