linux-kernel - [PATCH v4 00/11] KVM: x86/mmu: Make tdp

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Date:   Wed, 12 Oct 2022 18:16:51 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Matlack <dmatlack@...gle.com>,
        Isaku Yamahata <isaku.yamahata@...el.com>
Subject: [PATCH v4 00/11] KVM: x86/mmu: Make tdp_mmu a read-only parameter

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
-- 
2.38.0.rc1.362.ged0d419d3c-goog