On 11/2/2023 1:36 AM, Sean Christopherson wrote:
KVM_CAP_MEMORY_FAULT_INFO is x86 only, is it better to put this function to
<asm/kvm_host.h>?
I'd prefer to keep it in generic code, as it's highly likely to end up there
sooner than later. There's a known use case for ARM (exit to userspace on missing
userspace mapping[*]), and I'm guessing pKVM (also ARM) will also utilize this API.
[*]https://lore.kernel.org/all/20230908222905.1321305-8-amoorthy@xxxxxxxxxx
I wonder how this CAP is supposed to be checked in userspace, for guest
memfd case? something like this?
if (!kvm_check_extension(s, KVM_CAP_MEMORY_FAULT_INFO) &&
run->exit_reason == KVM_EXIT_MEMORY_FAULT)
abort("unexpected KVM_EXIT_MEMORY_FAULT");
In my implementation of QEMU patches, I find it's unnecessary. When
userspace gets an exit with KVM_EXIT_MEMORY_FAULT, it implies
"KVM_CAP_MEMORY_FAULT_INFO".
So I don't see how it is necessary in this series. Whether it's
necessary or not for [*], I don't have the answer but we can leave the
discussion to that patch series.
