lkml.org 
[lkml]   [2021]   [Jul]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC PATCH v2 16/69] KVM: x86/mmu: Zap only leaf SPTEs for deleted/moved memslot by default
From
Date
On 03/07/21 00:04, isaku.yamahata@intel.com wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
>
> Zap only leaf SPTEs when deleting/moving a memslot by default, and add a
> module param to allow reverting to the old behavior of zapping all SPTEs
> at all levels and memslots when any memslot is updated.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
> arch/x86/kvm/mmu/mmu.c | 21 ++++++++++++++++++++-
> 1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 8d5876dfc6b7..5b8a640f8042 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -85,6 +85,9 @@ __MODULE_PARM_TYPE(nx_huge_pages_recovery_ratio, "uint");
> static bool __read_mostly force_flush_and_sync_on_reuse;
> module_param_named(flush_on_reuse, force_flush_and_sync_on_reuse, bool, 0644);
>
> +static bool __read_mostly memslot_update_zap_all;
> +module_param(memslot_update_zap_all, bool, 0444);
> +
> /*
> * When setting this variable to true it enables Two-Dimensional-Paging
> * where the hardware walks 2 page tables:
> @@ -5480,11 +5483,27 @@ static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm)
> return unlikely(!list_empty_careful(&kvm->arch.zapped_obsolete_pages));
> }
>
> +static void kvm_mmu_zap_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
> +{
> + /*
> + * Zapping non-leaf SPTEs, a.k.a. not-last SPTEs, isn't required, worst
> + * case scenario we'll have unused shadow pages lying around until they
> + * are recycled due to age or when the VM is destroyed.
> + */
> + write_lock(&kvm->mmu_lock);
> + slot_handle_level(kvm, slot, kvm_zap_rmapp, PG_LEVEL_4K,
> + KVM_MAX_HUGEPAGE_LEVEL, true);
> + write_unlock(&kvm->mmu_lock);
> +}
> +
> static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm,
> struct kvm_memory_slot *slot,
> struct kvm_page_track_notifier_node *node)
> {
> - kvm_mmu_zap_all_fast(kvm);
> + if (memslot_update_zap_all)
> + kvm_mmu_zap_all_fast(kvm);
> + else
> + kvm_mmu_zap_memslot(kvm, slot);
> }
>
> void kvm_mmu_init_vm(struct kvm *kvm)
>

This is the old patch that broke VFIO for some unknown reason. The
commit message should at least say why memslot_update_zap_all is not
true by default. Also, IIUC the bug still there with NX hugepage splits
disabled, but what if the TDP MMU is enabled?

Paolo

\
 
 \ /
  Last update: 2021-07-06 16:38    [W:0.953 / U:0.656 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site