Re: [PATCH v2 0/9] KVM: x86/MMU: Optimize disabling dirty logging

Paolo Bonzini
2022-03-25T12:00:41Z

On 3/21/22 23:43, Ben Gardon wrote:
> Currently disabling dirty logging with the TDP MMU is extremely slow.
> On a 96 vCPU / 96G VM it takes ~256 seconds to disable dirty logging
> with the TDP MMU, as opposed to ~4 seconds with the legacy MMU. This
> series optimizes TLB flushes and introduces in-place large page
> promotion, to bring the disable dirty log time down to ~3 seconds.
>
> Testing:
> Ran KVM selftests and kvm-unit-tests on an Intel Haswell. This
> series introduced no new failures.

Thanks, looks good. The one change I'd make is to just place the
outcome of build_tdp_shadow_zero_bits_mask() in a global (say
tdp_shadow_zero_check) at kvm_configure_mmu() time. The
tdp_max_root_level works as a conservative choice for the second
argument of build_tdp_shadow_zero_bits_mask().

No need to do anything though, I'll handle this later in 5.19 time (and
first merge my changes that factor out the constant part of
vcpu->arch.root_mmu initialization, since this is part of the same ideas).

Paolo