Messages in this thread | | | Date | Thu, 21 Sep 2023 12:52:40 +0200 | Subject | Re: [PATCH 2/3] KVM: x86/mmu: Take "shared" instead of "as_id" TDP MMU's yield-safe iterator | From | Paolo Bonzini <> |
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On 9/16/23 02:39, Sean Christopherson wrote: > Replace the address space ID in for_each_tdp_mmu_root_yield_safe() with a > shared (vs. exclusive) param, and have the walker iterate over all address > spaces as all callers want to process all address spaces. Drop the @as_id > param as well as the manual address space iteration in callers. > > Add the @shared param even though the two current callers pass "false" > unconditionally, as the main reason for refactoring the walker is to > simplify using it to zap invalid TDP MMU roots, which is done with > mmu_lock held for read. > > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson <seanjc@google.com>
You konw what, I don't really like the "bool shared" arguments anymore. For example, neither tdp_mmu_next_root nor kvm_tdp_mmu_put_root need to know if the lock is taken for read or write; protection is achieved via RCU and tdp_mmu_pages_lock. It's more self-documenting to remove the argument and assert that the lock is taken.
Likewise, the argument is more or less unnecessary in the for_each_*_tdp_mmu_root_yield_safe() macros. Many users check for the lock before calling it; and all of them either call small functions that do the check, or end up calling tdp_mmu_set_spte_atomic() and tdp_mmu_iter_set_spte(), so the per-iteration checks are also overkill.
It may be useful to a few assertions to make up for the lost check before the first execution of the body of for_each_*_tdp_mmu_root_yield_safe(), but even this is more for documentation reasons than to catch actual bugs.
I'll send a v2.
Paolo
> --- > arch/x86/kvm/mmu/mmu.c | 8 ++------ > arch/x86/kvm/mmu/tdp_mmu.c | 20 ++++++++++---------- > arch/x86/kvm/mmu/tdp_mmu.h | 3 +-- > 3 files changed, 13 insertions(+), 18 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 59f5e40b8f55..54f94f644b42 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -6246,7 +6246,6 @@ static bool kvm_rmap_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_e > void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end) > { > bool flush; > - int i; > > if (WARN_ON_ONCE(gfn_end <= gfn_start)) > return; > @@ -6257,11 +6256,8 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end) > > flush = kvm_rmap_zap_gfn_range(kvm, gfn_start, gfn_end); > > - if (tdp_mmu_enabled) { > - for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) > - flush = kvm_tdp_mmu_zap_leafs(kvm, i, gfn_start, > - gfn_end, flush); > - } > + if (tdp_mmu_enabled) > + flush = kvm_tdp_mmu_zap_leafs(kvm, gfn_start, gfn_end, flush); > > if (flush) > kvm_flush_remote_tlbs_range(kvm, gfn_start, gfn_end - gfn_start); > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index 89aaa2463373..7cb1902ae032 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -211,8 +211,12 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm, > #define for_each_valid_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared) \ > __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, true) > > -#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id) \ > - __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, false, false) > +#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _shared) \ > + for (_root = tdp_mmu_next_root(_kvm, NULL, _shared, false); \ > + _root; \ > + _root = tdp_mmu_next_root(_kvm, _root, _shared, false)) \ > + if (!kvm_lockdep_assert_mmu_lock_held(_kvm, _shared)) { \ > + } else > > /* > * Iterate over all TDP MMU roots. Requires that mmu_lock be held for write, > @@ -877,12 +881,11 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root, > * true if a TLB flush is needed before releasing the MMU lock, i.e. if one or > * more SPTEs were zapped since the MMU lock was last acquired. > */ > -bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end, > - bool flush) > +bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, gfn_t start, gfn_t end, bool flush) > { > struct kvm_mmu_page *root; > > - for_each_tdp_mmu_root_yield_safe(kvm, root, as_id) > + for_each_tdp_mmu_root_yield_safe(kvm, root, false) > flush = tdp_mmu_zap_leafs(kvm, root, start, end, true, flush); > > return flush; > @@ -891,7 +894,6 @@ bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end, > void kvm_tdp_mmu_zap_all(struct kvm *kvm) > { > struct kvm_mmu_page *root; > - int i; > > /* > * Zap all roots, including invalid roots, as all SPTEs must be dropped > @@ -905,10 +907,8 @@ void kvm_tdp_mmu_zap_all(struct kvm *kvm) > * is being destroyed or the userspace VMM has exited. In both cases, > * KVM_RUN is unreachable, i.e. no vCPUs will ever service the request. > */ > - for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { > - for_each_tdp_mmu_root_yield_safe(kvm, root, i) > - tdp_mmu_zap_root(kvm, root, false); > - } > + for_each_tdp_mmu_root_yield_safe(kvm, root, false) > + tdp_mmu_zap_root(kvm, root, false); > } > > /* > diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h > index eb4fa345d3a4..bc088953f929 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.h > +++ b/arch/x86/kvm/mmu/tdp_mmu.h > @@ -20,8 +20,7 @@ __must_check static inline bool kvm_tdp_mmu_get_root(struct kvm_mmu_page *root) > void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root, > bool shared); > > -bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end, > - bool flush); > +bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, gfn_t start, gfn_t end, bool flush); > bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp); > void kvm_tdp_mmu_zap_all(struct kvm *kvm); > void kvm_tdp_mmu_invalidate_all_roots(struct kvm *kvm);
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