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KVM: TDX: Reject fully in-kernel irqchip if EOIs are protected, i.e. for TDX VMs

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Reject KVM_CREATE_IRQCHIP if the VM type has protected EOIs, i.e. if KVM
can't intercept EOI and thus can't faithfully emulate level-triggered
interrupts that are routed through the I/O APIC.  For TDX VMs, the
TDX-Module owns the VMX EOI-bitmap and configures all IRQ vectors to have
the CPU accelerate EOIs, i.e. doesn't allow KVM to intercept any EOIs.

KVM already requires a split irqchip[1], but does so during vCPU creation,
which is both too late to allow userspace to fallback to a split irqchip
and a less-than-stellar experience for userspace since an -EINVAL on
KVM_VCPU_CREATE is far harder to debug/triage than failure exactly on
KVM_CREATE_IRQCHIP.  And of course, allowing an action that ultimately
fails is arguably a bug regardless of the impact on userspace.

Link: https://lore.kernel.org/lkml/20250222014757.897978-11-binbin.wu@linux.intel.com [1]
Link: https://lore.kernel.org/lkml/aK3vZ5HuKKeFuuM4@google.com
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sagi Shahar <sagis@google.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20250827011726.2451115-1-sagis@google.com
[sean: massage shortlog+changelog, relocate setting has_protected_eoi]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sagi Shahar 2025-08-26 18:17:26 -07:00 committed by Sean Christopherson
parent aac057dd62
commit b3a37bff8d
3 changed files with 15 additions and 0 deletions
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1
arch/x86/include/asm/kvm_host.h
View File

@ -1362,6 +1362,7 @@ struct kvm_arch {
u8 vm_type;
bool has_private_mem;
bool has_protected_state;
bool has_protected_eoi;
bool pre_fault_allowed;
struct hlist_head *mmu_page_hash;
struct list_head active_mmu_pages;

5
arch/x86/kvm/vmx/tdx.c
View File

@ -629,6 +629,11 @@ int tdx_vm_init(struct kvm *kvm)
struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
kvm->arch.has_protected_state = true;
/*
* TDX Module doesn't allow the hypervisor to modify the EOI-bitmap,
* i.e. all EOIs are accelerated and never trigger exits.
*/
kvm->arch.has_protected_eoi = true;
kvm->arch.has_private_mem = true;
kvm->arch.disabled_quirks |= KVM_X86_QUIRK_IGNORE_GUEST_PAT;

9
arch/x86/kvm/x86.c
View File

@ -6989,6 +6989,15 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
if (irqchip_in_kernel(kvm))
goto create_irqchip_unlock;
/*
* Disallow an in-kernel I/O APIC if the VM has protected EOIs,
* i.e. if KVM can't intercept EOIs and thus can't properly
* emulate level-triggered interrupts.
*/
r = -ENOTTY;
if (kvm->arch.has_protected_eoi)
goto create_irqchip_unlock;
r = -EINVAL;
if (kvm->created_vcpus)
goto create_irqchip_unlock;