linux-kernel - Re: [PATCH v3 00/31] KVM: x86: pass arguments on the page fault path via struct kvm_page

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Date:   Tue, 28 Sep 2021 23:27:39 +0000
From:   David Matlack <dmatlack@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        seanjc@...gle.com
Subject: Re: [PATCH v3 00/31] KVM: x86: pass arguments on the page fault path
 via struct kvm_page_fault

On Fri, Sep 24, 2021 at 12:31:21PM -0400, Paolo Bonzini wrote:
> The current kvm page fault handlers passes around many arguments to the
> functions.  To simplify those arguments and local variables, introduce
> a data structure, struct kvm_page_fault, to hold those arguments and
> variables.  struct kvm_page_fault is allocated on stack on the caller
> of kvm fault handler, kvm_mmu_do_page_fault(), and passed around.
> 
> Later in the series, my patches are interleaved with David's work to
> add the memory slot to the struct and avoid repeated lookups.  Along the
> way you will find some cleanups of functions with a ludicrous number of
> arguments, so that they use struct kvm_page_fault as much as possible
> or at least receive related information from a single argument.  make_spte
> in particular goes from 11 to 10 arguments (yeah I know) despite gaining
> two for kvm_mmu_page and kvm_memory_slot.
> 
> This can be sometimes a bit debatable (for example struct kvm_mmu_page
> is used a little more on the TDP MMU paths), but overall I think the
> result is an improvement.  For example the SET_SPTE_* constants go
> away, and they absolutely didn't belong in the TDP MMU.  But if you
> disagree with some of the changes, please speak up loudly!

Thanks for getting this cleaned up and sent out. The series looks good
overall. I had 2 small comments but otherwise:

Reviewed-by: David Matlack <dmatlack@...gle.com>

> 
> Testing: survives kvm-unit-tests on Intel with all of ept=0, ept=1
> tdp_mmu=0, ept=1.  Will do more before committing to it in kvm/next of
> course.
> 
> Paolo
> 
> David Matlack (5):
>   KVM: x86/mmu: Fold rmap_recycle into rmap_add
>   KVM: x86/mmu: Pass the memslot around via struct kvm_page_fault
>   KVM: x86/mmu: Avoid memslot lookup in page_fault_handle_page_track
>   KVM: x86/mmu: Avoid memslot lookup in rmap_add
>   KVM: x86/mmu: Avoid memslot lookup in make_spte and
>     mmu_try_to_unsync_pages
> 
> Paolo Bonzini (25):
>   KVM: MMU: pass unadulterated gpa to direct_page_fault
>   KVM: MMU: Introduce struct kvm_page_fault
>   KVM: MMU: change mmu->page_fault() arguments to kvm_page_fault
>   KVM: MMU: change direct_page_fault() arguments to kvm_page_fault
>   KVM: MMU: change page_fault_handle_page_track() arguments to
>     kvm_page_fault
>   KVM: MMU: change kvm_faultin_pfn() arguments to kvm_page_fault
>   KVM: MMU: change handle_abnormal_pfn() arguments to kvm_page_fault
>   KVM: MMU: change __direct_map() arguments to kvm_page_fault
>   KVM: MMU: change FNAME(fetch)() arguments to kvm_page_fault
>   KVM: MMU: change kvm_tdp_mmu_map() arguments to kvm_page_fault
>   KVM: MMU: change tdp_mmu_map_handle_target_level() arguments to
>     kvm_page_fault
>   KVM: MMU: change fast_page_fault() arguments to kvm_page_fault
>   KVM: MMU: change kvm_mmu_hugepage_adjust() arguments to kvm_page_fault
>   KVM: MMU: change disallowed_hugepage_adjust() arguments to
>     kvm_page_fault
>   KVM: MMU: change tracepoints arguments to kvm_page_fault
>   KVM: MMU: mark page dirty in make_spte
>   KVM: MMU: unify tdp_mmu_map_set_spte_atomic and
>     tdp_mmu_set_spte_atomic_no_dirty_log
>   KVM: MMU: inline set_spte in mmu_set_spte
>   KVM: MMU: inline set_spte in FNAME(sync_page)
>   KVM: MMU: clean up make_spte return value
>   KVM: MMU: remove unnecessary argument to mmu_set_spte
>   KVM: MMU: set ad_disabled in TDP MMU role
>   KVM: MMU: pass kvm_mmu_page struct to make_spte
>   KVM: MMU: pass struct kvm_page_fault to mmu_set_spte
>   KVM: MMU: make spte an in-out argument in make_spte
> 
> Sean Christopherson (1):
>   KVM: x86/mmu: Verify shadow walk doesn't terminate early in page
>     faults
> 
>  arch/x86/include/asm/kvm_host.h       |   4 +-
>  arch/x86/include/asm/kvm_page_track.h |   4 +-
>  arch/x86/kvm/mmu.h                    |  84 +++++-
>  arch/x86/kvm/mmu/mmu.c                | 408 +++++++++++---------------
>  arch/x86/kvm/mmu/mmu_internal.h       |  22 +-
>  arch/x86/kvm/mmu/mmutrace.h           |  18 +-
>  arch/x86/kvm/mmu/page_track.c         |   6 +-
>  arch/x86/kvm/mmu/paging_tmpl.h        | 137 +++++----
>  arch/x86/kvm/mmu/spte.c               |  29 +-
>  arch/x86/kvm/mmu/spte.h               |  14 +-
>  arch/x86/kvm/mmu/tdp_mmu.c            | 123 +++-----
>  arch/x86/kvm/mmu/tdp_mmu.h            |   4 +-
>  12 files changed, 390 insertions(+), 463 deletions(-)
> 
> -- 
> 2.27.0
>