Sheng Yang wrote: > >>> return kvm; >>> } >>> >>> diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c >>> index 42e7fad..89007b2 100644 >>> --- a/drivers/kvm/vmx.c >>> +++ b/drivers/kvm/vmx.c >>> @@ -1466,6 +1466,8 @@ static int alloc_apic_access_page(struct kvm *kvm) >>> int r; >>> >>> r = -EFAULT; >>> + if (kvm->apic_access_page) >>> + return 0; >>> >> Racy, what if two vcpus are created simultaneously? >> > > I think it is not racy, for BSP have been created before APs in sequence, and > I am ensure only BSP(vcpu id=0) would call this. > >
That's true for qemu. But we have to be use malicious userspace can't crash the kernel or leak memory using the kvm APIs. >>> kvm_userspace_mem.slot = APIC_ACCESS_PAGE_PRIVATE_MEMSLOT; >>> kvm_userspace_mem.flags = 0; >>> kvm_userspace_mem.guest_phys_addr = 0xfee00000ULL; >>> @@ -1584,7 +1586,8 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx) >>> vmcs_writel(CR0_GUEST_HOST_MASK, ~0UL); >>> vmcs_writel(CR4_GUEST_HOST_MASK, KVM_GUEST_CR4_MASK); >>> >>> - if (vm_need_virtualize_apic_accesses(vmx->vcpu.kvm)) >>> + if ((vmx->vcpu.vcpu_id == 0) && >>> + (vm_need_virtualize_apic_accesses(vmx->vcpu.kvm))) >>> if (alloc_apic_access_page(vmx->vcpu.kvm) != 0) >>> return -ENOMEM; >>> >> We may not have vcpu id 0 (though it's very unlikely). >> > > Um... I am not quite understand when we will miss vcpu id 0. I think vcpu id > 0 > is used to indicate BSP. > That's what qemu does. But another userspace perhaps will do this differently. This is a minor problem compared to the one above. > >> I think the problems arise because we are doing a VM-wide operation >> (memory slot) from a vcpu context. I think adding a ->vm_create() arch >> op and allocating the memory there will be better (under kvm->lock). >> > > Agree, but a little problem remains. > > I have to do feature detection before call allocate function, but > kvm_create_vm() is called before kvm_create_irqchip(). So I can't find a > proper position for create_vm(). Any suggestion? > You're right, during vm creation we have no idea if we want the FlexPriority page. So you can do this in the same place, just take kvm->mutex and check if it exists first (you need to do that anyway), no dependency on vcpu 0. -- Any sufficiently difficult bug is indistinguishable from a feature. ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
