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Message-ID: <CA+EHjTzz2PftRAFU9pQaE1D=E3hwBDCDQpJ69O6r5akdAs0Exw@mail.gmail.com>
Date: Thu, 2 Nov 2023 13:55:42 +0000
From: Fuad Tabba <tabba@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
Oliver Upton <oliver.upton@...ux.dev>,
Huacai Chen <chenhuacai@...nel.org>,
Michael Ellerman <mpe@...erman.id.au>,
Anup Patel <anup@...infault.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>, kvm@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>,
Xu Yilun <yilun.xu@...el.com>,
Chao Peng <chao.p.peng@...ux.intel.com>,
Jarkko Sakkinen <jarkko@...nel.org>,
Anish Moorthy <amoorthy@...gle.com>,
David Matlack <dmatlack@...gle.com>,
Yu Zhang <yu.c.zhang@...ux.intel.com>,
Isaku Yamahata <isaku.yamahata@...el.com>,
Mickaël Salaün <mic@...ikod.net>,
Vlastimil Babka <vbabka@...e.cz>,
Vishal Annapurve <vannapurve@...gle.com>,
Ackerley Tng <ackerleytng@...gle.com>,
Maciej Szmigiero <mail@...iej.szmigiero.name>,
David Hildenbrand <david@...hat.com>,
Quentin Perret <qperret@...gle.com>,
Michael Roth <michael.roth@....com>,
Wang <wei.w.wang@...el.com>,
Liam Merwick <liam.merwick@...cle.com>,
Isaku Yamahata <isaku.yamahata@...il.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v13 11/35] KVM: Drop .on_unlock() mmu_notifier hook
On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Drop the .on_unlock() mmu_notifer hook now that it's no longer used for
> notifying arch code that memory has been reclaimed. Adding .on_unlock()
> and invoking it *after* dropping mmu_lock was a terrible idea, as doing so
> resulted in .on_lock() and .on_unlock() having divergent and asymmetric
> behavior, and set future developers up for failure, i.e. all but asked for
> bugs where KVM relied on using .on_unlock() to try to run a callback while
> holding mmu_lock.
>
> Opportunistically add a lockdep assertion in kvm_mmu_invalidate_end() to
> guard against future bugs of this nature.
>
> Reported-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Link: https://lore.kernel.org/all/20230802203119.GB2021422@ls.amr.corp.intel.com
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
Reviewed-by: Fuad Tabba <tabba@...gle.com>
Tested-by: Fuad Tabba <tabba@...gle.com>
Cheers,
/fuad
> virt/kvm/kvm_main.c | 13 +++----------
> 1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 2bc04c8ae1f4..cb9376833c18 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -544,7 +544,6 @@ static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
> typedef bool (*gfn_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range);
>
> typedef void (*on_lock_fn_t)(struct kvm *kvm);
> -typedef void (*on_unlock_fn_t)(struct kvm *kvm);
>
> struct kvm_mmu_notifier_range {
> /*
> @@ -556,7 +555,6 @@ struct kvm_mmu_notifier_range {
> union kvm_mmu_notifier_arg arg;
> gfn_handler_t handler;
> on_lock_fn_t on_lock;
> - on_unlock_fn_t on_unlock;
> bool flush_on_ret;
> bool may_block;
> };
> @@ -663,11 +661,8 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,
> if (range->flush_on_ret && r.ret)
> kvm_flush_remote_tlbs(kvm);
>
> - if (r.found_memslot) {
> + if (r.found_memslot)
> KVM_MMU_UNLOCK(kvm);
> - if (!IS_KVM_NULL_FN(range->on_unlock))
> - range->on_unlock(kvm);
> - }
>
> srcu_read_unlock(&kvm->srcu, idx);
>
> @@ -687,7 +682,6 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn,
> .arg = arg,
> .handler = handler,
> .on_lock = (void *)kvm_null_fn,
> - .on_unlock = (void *)kvm_null_fn,
> .flush_on_ret = true,
> .may_block = false,
> };
> @@ -706,7 +700,6 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn
> .end = end,
> .handler = handler,
> .on_lock = (void *)kvm_null_fn,
> - .on_unlock = (void *)kvm_null_fn,
> .flush_on_ret = false,
> .may_block = false,
> };
> @@ -813,7 +806,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> .end = range->end,
> .handler = kvm_mmu_unmap_gfn_range,
> .on_lock = kvm_mmu_invalidate_begin,
> - .on_unlock = (void *)kvm_null_fn,
> .flush_on_ret = true,
> .may_block = mmu_notifier_range_blockable(range),
> };
> @@ -858,6 +850,8 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>
> void kvm_mmu_invalidate_end(struct kvm *kvm)
> {
> + lockdep_assert_held_write(&kvm->mmu_lock);
> +
> /*
> * This sequence increase will notify the kvm page fault that
> * the page that is going to be mapped in the spte could have
> @@ -889,7 +883,6 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
> .end = range->end,
> .handler = (void *)kvm_null_fn,
> .on_lock = kvm_mmu_invalidate_end,
> - .on_unlock = (void *)kvm_null_fn,
> .flush_on_ret = false,
> .may_block = mmu_notifier_range_blockable(range),
> };
> --
> 2.42.0.820.g83a721a137-goog
>
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