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Message-ID: <CA+EHjTy5+Ke_7Uh72p--H9kGcE-PK4EVmp7ym6Q1-PO28u6CCQ@mail.gmail.com>
Date: Mon, 5 Dec 2022 09:23:49 +0000
From: Fuad Tabba <tabba@...gle.com>
To: Chao Peng <chao.p.peng@...ux.intel.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
Paolo Bonzini <pbonzini@...hat.com>,
Jonathan Corbet <corbet@....net>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Arnd Bergmann <arnd@...db.de>,
Naoya Horiguchi <naoya.horiguchi@....com>,
Miaohe Lin <linmiaohe@...wei.com>, x86@...nel.org,
"H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
Jeff Layton <jlayton@...nel.org>,
"J . Bruce Fields" <bfields@...ldses.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
Steven Price <steven.price@....com>,
"Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
Vlastimil Babka <vbabka@...e.cz>,
Vishal Annapurve <vannapurve@...gle.com>,
Yu Zhang <yu.c.zhang@...ux.intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
ddutile@...hat.com, dhildenb@...hat.com,
Quentin Perret <qperret@...gle.com>,
Michael Roth <michael.roth@....com>, mhocko@...e.com,
wei.w.wang@...el.com
Subject: Re: [PATCH v10 5/9] KVM: Use gfn instead of hva for mmu_notifier_retry
Hi Chao,
On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@...ux.intel.com> wrote:
>
> Currently in mmu_notifier invalidate path, hva range is recorded and
> then checked against by mmu_notifier_retry_hva() in the page fault
> handling path. However, for the to be introduced private memory, a page
> fault may not have a hva associated, checking gfn(gpa) makes more sense.
>
> For existing hva based shared memory, gfn is expected to also work. The
> only downside is when aliasing multiple gfns to a single hva, the
> current algorithm of checking multiple ranges could result in a much
> larger range being rejected. Such aliasing should be uncommon, so the
> impact is expected small.
>
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
> ---
> arch/x86/kvm/mmu/mmu.c | 8 +++++---
> include/linux/kvm_host.h | 33 +++++++++++++++++++++------------
> virt/kvm/kvm_main.c | 32 +++++++++++++++++++++++---------
> 3 files changed, 49 insertions(+), 24 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 4736d7849c60..e2c70b5afa3e 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4259,7 +4259,7 @@ static bool is_page_fault_stale(struct kvm_vcpu *vcpu,
> return true;
>
> return fault->slot &&
> - mmu_invalidate_retry_hva(vcpu->kvm, mmu_seq, fault->hva);
> + mmu_invalidate_retry_gfn(vcpu->kvm, mmu_seq, fault->gfn);
> }
>
> static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> @@ -6098,7 +6098,9 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
>
> write_lock(&kvm->mmu_lock);
>
> - kvm_mmu_invalidate_begin(kvm, gfn_start, gfn_end);
> + kvm_mmu_invalidate_begin(kvm);
> +
> + kvm_mmu_invalidate_range_add(kvm, gfn_start, gfn_end);
>
> flush = kvm_rmap_zap_gfn_range(kvm, gfn_start, gfn_end);
>
> @@ -6112,7 +6114,7 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
> kvm_flush_remote_tlbs_with_address(kvm, gfn_start,
> gfn_end - gfn_start);
>
> - kvm_mmu_invalidate_end(kvm, gfn_start, gfn_end);
> + kvm_mmu_invalidate_end(kvm);
>
> write_unlock(&kvm->mmu_lock);
> }
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 02347e386ea2..3d69484d2704 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -787,8 +787,8 @@ struct kvm {
> struct mmu_notifier mmu_notifier;
> unsigned long mmu_invalidate_seq;
> long mmu_invalidate_in_progress;
> - unsigned long mmu_invalidate_range_start;
> - unsigned long mmu_invalidate_range_end;
> + gfn_t mmu_invalidate_range_start;
> + gfn_t mmu_invalidate_range_end;
> #endif
> struct list_head devices;
> u64 manual_dirty_log_protect;
> @@ -1389,10 +1389,9 @@ void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc);
> void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> #endif
>
> -void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> - unsigned long end);
> -void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
> - unsigned long end);
> +void kvm_mmu_invalidate_begin(struct kvm *kvm);
> +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end);
> +void kvm_mmu_invalidate_end(struct kvm *kvm);
>
> long kvm_arch_dev_ioctl(struct file *filp,
> unsigned int ioctl, unsigned long arg);
> @@ -1963,9 +1962,9 @@ static inline int mmu_invalidate_retry(struct kvm *kvm, unsigned long mmu_seq)
> return 0;
> }
>
> -static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
> +static inline int mmu_invalidate_retry_gfn(struct kvm *kvm,
> unsigned long mmu_seq,
> - unsigned long hva)
> + gfn_t gfn)
> {
> lockdep_assert_held(&kvm->mmu_lock);
> /*
> @@ -1974,10 +1973,20 @@ static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
> * that might be being invalidated. Note that it may include some false
nit: "might be" (or) "is being"
> * positives, due to shortcuts when handing concurrent invalidations.
nit: handling
> */
> - if (unlikely(kvm->mmu_invalidate_in_progress) &&
> - hva >= kvm->mmu_invalidate_range_start &&
> - hva < kvm->mmu_invalidate_range_end)
> - return 1;
> + if (unlikely(kvm->mmu_invalidate_in_progress)) {
> + /*
> + * Dropping mmu_lock after bumping mmu_invalidate_in_progress
> + * but before updating the range is a KVM bug.
> + */
> + if (WARN_ON_ONCE(kvm->mmu_invalidate_range_start == INVALID_GPA ||
> + kvm->mmu_invalidate_range_end == INVALID_GPA))
INVALID_GPA is an x86-specific define in
arch/x86/include/asm/kvm_host.h, so this doesn't build on other
architectures. The obvious fix is to move it to
include/linux/kvm_host.h.
Cheers,
/fuad
> + return 1;
> +
> + if (gfn >= kvm->mmu_invalidate_range_start &&
> + gfn < kvm->mmu_invalidate_range_end)
> + return 1;
> + }
> +
> if (kvm->mmu_invalidate_seq != mmu_seq)
> return 1;
> return 0;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index b882eb2c76a2..ad55dfbc75d7 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -540,9 +540,7 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn,
>
> typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range);
>
> -typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start,
> - unsigned long end);
> -
> +typedef void (*on_lock_fn_t)(struct kvm *kvm);
> typedef void (*on_unlock_fn_t)(struct kvm *kvm);
>
> struct kvm_hva_range {
> @@ -628,7 +626,8 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
> locked = true;
> KVM_MMU_LOCK(kvm);
> if (!IS_KVM_NULL_FN(range->on_lock))
> - range->on_lock(kvm, range->start, range->end);
> + range->on_lock(kvm);
> +
> if (IS_KVM_NULL_FN(range->handler))
> break;
> }
> @@ -715,8 +714,7 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
> kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
> }
>
> -void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> - unsigned long end)
> +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> {
> /*
> * The count increase must become visible at unlock time as no
> @@ -724,6 +722,17 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> * count is also read inside the mmu_lock critical section.
> */
> kvm->mmu_invalidate_in_progress++;
> +
> + if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> + kvm->mmu_invalidate_range_start = INVALID_GPA;
> + kvm->mmu_invalidate_range_end = INVALID_GPA;
> + }
> +}
> +
> +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> + WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> +
> if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> kvm->mmu_invalidate_range_start = start;
> kvm->mmu_invalidate_range_end = end;
> @@ -744,6 +753,12 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> }
> }
>
> +static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> +{
> + kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> + return kvm_unmap_gfn_range(kvm, range);
> +}
> +
> static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> const struct mmu_notifier_range *range)
> {
> @@ -752,7 +767,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> .start = range->start,
> .end = range->end,
> .pte = __pte(0),
> - .handler = kvm_unmap_gfn_range,
> + .handler = kvm_mmu_unmap_gfn_range,
> .on_lock = kvm_mmu_invalidate_begin,
> .on_unlock = kvm_arch_guest_memory_reclaimed,
> .flush_on_ret = true,
> @@ -791,8 +806,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> return 0;
> }
>
> -void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
> - unsigned long end)
> +void kvm_mmu_invalidate_end(struct kvm *kvm)
> {
> /*
> * This sequence increase will notify the kvm page fault that
> --
> 2.25.1
>
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