> On Mar 7, 2020, at 2:09 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > Andy Lutomirski <luto@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx >> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx> >> --- >> 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. Indeed. But read v2 please. > > See also my reply in the other thread: > > https://lore.kernel.org/r/87r1y4a3gw.fsf@xxxxxxxxxxxxxxxxxxxxxxx > > Thanks, > > tglx
