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Message-ID: <adebc422-2937-48d7-20c1-aef2dc1ac436@redhat.com>
Date: Thu, 21 Sep 2023 12:52:40 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Pattara Teerapong <pteerapong@...gle.com>,
David Stevens <stevensd@...gle.com>,
Yiwei Zhang <zzyiwei@...gle.com>,
Paul Hsia <paulhsia@...gle.com>
Subject: Re: [PATCH 2/3] KVM: x86/mmu: Take "shared" instead of "as_id" TDP
MMU's yield-safe iterator
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@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.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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