Andy Lutomirski luto@kernel.org writes:
The ABI is broken and we cannot support it properly. Turn it off.
If this causes a meaningful performance regression for someone, KVM can introduce an improved ABI that is supportable.
Cc: stable@vger.kernel.org Signed-off-by: Andy Lutomirski luto@kernel.org
arch/x86/kernel/kvm.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 93ab0cbd304e..71f9f39f93da 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -318,11 +318,16 @@ static void kvm_guest_cpu_init(void) pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason)); -#ifdef CONFIG_PREEMPTION
pa |= KVM_ASYNC_PF_SEND_ALWAYS;-#endif pa |= KVM_ASYNC_PF_ENABLED;
/** We do not set KVM_ASYNC_PF_SEND_ALWAYS. With the current* KVM paravirt ABI, if an async page fault occurs on an early* memory access in the normal (sync) #PF path or in an NMI* that happens early in the #PF code, the combination of CR2* and the APF reason field will be corrupted.
I don't think this can happen. In both cases IF == 0 and that async (think host side) page fault will be completely handled on the host. There is no injection happening in such a case ever. If it does, then yes the host side implementation is buggered, but AFAICT this is not the case.
See also my reply in the other thread:
https://lore.kernel.org/r/87r1y4a3gw.fsf@nanos.tec.linutronix.de
Thanks,
tglx