linux-kernel - Re: [RFC PATCH v2] KVM: x86/mmu: replace BUG() with KVM

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Message-ID: <CABgObfYpn98X2NFhoWNAPuyu_NtmovKD5MHoon0gtVP08Su0eA@mail.gmail.com>
Date:   Thu, 24 Nov 2022 02:16:54 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Mingwei Zhang <mizhang@...gle.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Nagareddy Reddy <nspreddy@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [RFC PATCH v2] KVM: x86/mmu: replace BUG() with KVM_BUG() in
 shadow mmu

> v1 -> v2:
>  - compile test the code.
>  - fill KVM_BUG() with kvm_get_running_vcpu()->kvm

Nope, the zapping code paths will run often with no running vCPU, for
example drop_parent_pte <- kvm_mmu_unlink_parents <-
__kvm_mmu_prepare_zap_page <- kvm_zap_obsolete_pages <-
kvm_mmu_zap_all_fast <- kvm_mmu_invalidate_zap_pages_in_memslot <-
kvm_page_track_flush_slot <- kvm_arch_flush_shadow_memslot <-
kvm_invalidate_memslot <- ioctl(KVM_SET_USER_MEMORY_REGION).

Paolo

> v1:
> https://lore.kernel.org/all/20221123231206.274392-1-mizhang@google.com/
>
> Cc: Nagareddy Reddy <nspreddy@...gle.com>
> Cc: Jim Mattson <jmattson@...gle.com>
> Cc: David Matlack <dmatlack@...gle.com>
> Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 4736d7849c60..f3b307c588ac 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -955,12 +955,12 @@ static void pte_list_remove(u64 *spte, struct kvm_rmap_head *rmap_head)
>
>         if (!rmap_head->val) {
>                 pr_err("%s: %p 0->BUG\n", __func__, spte);
> -               BUG();
> +               KVM_BUG(true, kvm_get_running_vcpu()->kvm, "");
>         } else if (!(rmap_head->val & 1)) {
>                 rmap_printk("%p 1->0\n", spte);
>                 if ((u64 *)rmap_head->val != spte) {
>                         pr_err("%s:  %p 1->BUG\n", __func__, spte);
> -                       BUG();
> +                       KVM_BUG(true, kvm_get_running_vcpu()->kvm, "");
>                 }
>                 rmap_head->val = 0;
>         } else {
> @@ -979,7 +979,7 @@ static void pte_list_remove(u64 *spte, struct kvm_rmap_head *rmap_head)
>                         desc = desc->more;
>                 }
>                 pr_err("%s: %p many->many\n", __func__, spte);
> -               BUG();
> +               KVM_BUG(true, kvm_get_running_vcpu()->kvm, "");
>         }
>  }
>
> --
> 2.38.1.584.g0f3c55d4c2-goog
>