[PATCH v4 00/11] KVM: x86/mmu: Make tdp_mmu a read-only parameter

Sean Christopherson
2022-10-12T18:17:27Z

This is a variation of David's series to change tdp_mmu to a RO param[*].
The key difference is that instead of moving the TDP MMU page fault handler
to its own function, use static branches to make TDP MMU page faults (and
a few other paths) effectively branch free.

I'm not dead set against having a dedicated TDP MMU page fault handler, but
IMO it's not really better once the TDP MMU vs. shadow MMU is reduced to a
static branch, just different. The read vs. write mmu_lock is the most
visible ugliness, and that can be buried in helpers if we really want to
make the page fault handler easier on the eyes, e.g.

direct_page_fault_mmu_lock(vcpu);

if (is_page_fault_stale(vcpu, fault))
goto out_unlock;

if (is_tdp_mmu_enabled()) {
r = kvm_tdp_mmu_map(vcpu, fault);
} else {
r = make_mmu_pages_available(vcpu);
if (r)
goto out_unlock;

r = __direct_map(vcpu, fault);
}

out_unlock:
direct_page_fault_mmu_unlock(vcpu);

v4:
- Keep is_tdp_mmu_page() in patch 1.
- Collect reviews. [Isaku]
- Skip "make MMU pages available" for root allocations.
- Rework "is TDP MMU" checks to take advantage of read-only param.
- Use a static key to track TDP MMU enabling.

[*] https://lkml.kernel.org/r/20220921173546.2674386-1-dmatlack@google.com

David Matlack (7):
KVM: x86/mmu: Change tdp_mmu to a read-only parameter
KVM: x86/mmu: Move TDP MMU VM init/uninit behind tdp_mmu_enabled
KVM: x86/mmu: Grab mmu_invalidate_seq in kvm_faultin_pfn()
KVM: x86/mmu: Handle error PFNs in kvm_faultin_pfn()
KVM: x86/mmu: Avoid memslot lookup during KVM_PFN_ERR_HWPOISON
handling
KVM: x86/mmu: Handle no-slot faults in kvm_faultin_pfn()
KVM: x86/mmu: Stop needlessly making MMU pages available for TDP MMU

Sean Christopherson (4):
KVM: x86/mmu: Pivot on "TDP MMU enabled" when handling direct page
faults
KVM: x86/mmu: Pivot on "TDP MMU enabled" to check if active MMU is TDP
MMU
KVM: x86/mmu: Replace open coded usage of tdp_mmu_page with
is_tdp_mmu_page()
KVM: x86/mmu: Use static key/branches for checking if TDP MMU is
enabled

arch/x86/include/asm/kvm_host.h | 9 --
arch/x86/kvm/mmu.h | 14 ++-
arch/x86/kvm/mmu/mmu.c | 212 ++++++++++++++++++++------------
arch/x86/kvm/mmu/mmu_internal.h | 1 +
arch/x86/kvm/mmu/paging_tmpl.h | 12 +-
arch/x86/kvm/mmu/tdp_mmu.c | 13 +-
arch/x86/kvm/mmu/tdp_mmu.h | 25 +---
7 files changed, 149 insertions(+), 137 deletions(-)

base-commit: e18d6152ff0f41b7f01f9817372022df04e0d354