On 8/19/22 18:21, David Matlack wrote:
On Wed, Aug 3, 2022 at 3:50 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
Fully re-evaluate whether or not MMIO caching can be enabled when SPTE
masks change; simply clearing enable_mmio_caching when a configuration
isn't compatible with caching fails to handle the scenario where the
masks are updated, e.g. by VMX for EPT or by SVM to account for the C-bit
location, and toggle compatibility from false=>true.
Snapshot the original module param so that re-evaluating MMIO caching
preserves userspace's desire to allow caching. Use a snapshot approach
so that enable_mmio_caching still reflects KVM's actual behavior.
Is updating module parameters to reflect the actual behavior (vs.
userspace desire) something we should do for all module parameters?
I am doing an unrelated refactor to the tdp_mmu module parameter and
noticed it is not updated e.g. if userspace loads kvm_intel with
ept=N.
If it is cheap/easy then yeah, updating the parameters is the right
thing to do. Generally, however, this is only done for
kvm_intel/kvm_amd modules that depend on hardware features, because they
are more important for debugging user issues. (Or at least they were
until vmx features were added to /proc/cpuinfo).
Paolo
