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From: Binbin Wu <binbin.wu@linux.intel.com>
To: Sean Christopherson <seanjc@google.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Paolo Bonzini <pbonzini@redhat.com>,
	Michael Roth <michael.roth@amd.com>
Subject: Re: [PATCH 07/13] KVM: x86/mmu: Track PRIVATE impact on hugepage mappings for all memslots
Date: Wed, 27 Sep 2023 14:01:59 +0800	[thread overview]
Message-ID: <303a3382-32e7-6afd-bdfa-1cefdbdfb41e@linux.intel.com> (raw)
In-Reply-To: <20230921203331.3746712-8-seanjc@google.com>



On 9/22/2023 4:33 AM, Sean Christopherson wrote:
> Track the effects of private attributes on potential hugepage mappings if
> the VM supports private memory, i.e. even if the target memslot can only
> ever be mapped shared.  If userspace configures a chunk of memory as
> private, KVM must not allow that memory to be mapped shared regardless of
> whether or not the *current* memslot can be mapped private.  E.g. if the
> guest accesses a private range using a shared memslot, then KVM must exit
> to userspace.
How does usersapce handle this case?
IIRC, in gmem v12 patch set, it says a memslot can not be convert to 
private from shared.
So, userspace should delete the old memslot and and a new one?


> Fixes: 5bb0b4e162d1 ("KVM: x86: Disallow hugepages when memory attributes are mixed")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/x86/kvm/mmu/mmu.c | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 269d4dc47c98..148931cf9dba 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -7314,10 +7314,12 @@ bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
>   	lockdep_assert_held(&kvm->slots_lock);
>   
>   	/*
> -	 * KVM x86 currently only supports KVM_MEMORY_ATTRIBUTE_PRIVATE, skip
> -	 * the slot if the slot will never consume the PRIVATE attribute.
> +	 * Calculate which ranges can be mapped with hugepages even if the slot
> +	 * can't map memory PRIVATE.  KVM mustn't create a SHARED hugepage over
> +	 * a range that has PRIVATE GFNs, and conversely converting a range to
> +	 * SHARED may now allow hugepages.
>   	 */
> -	if (!kvm_slot_can_be_private(slot))
> +	if (WARN_ON_ONCE(!kvm_arch_has_private_mem(kvm)))
>   		return false;
>   
>   	/*
> @@ -7372,7 +7374,7 @@ void kvm_mmu_init_memslot_memory_attributes(struct kvm *kvm,
>   {
>   	int level;
>   
> -	if (!kvm_slot_can_be_private(slot))
> +	if (!kvm_arch_has_private_mem(kvm))
>   		return;
>   
>   	for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {


  reply	other threads:[~2023-09-27  6:03 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-21 20:33 [PATCH 00/13] KVM: guest_memfd fixes Sean Christopherson
2023-09-21 20:33 ` [PATCH 01/13] KVM: Assert that mmu_invalidate_in_progress *never* goes negative Sean Christopherson
2023-09-21 20:33 ` [PATCH 02/13] KVM: Actually truncate the inode when doing PUNCH_HOLE for guest_memfd Sean Christopherson
2023-09-21 20:33 ` [PATCH 03/13] KVM: WARN if *any* MMU invalidation sequence doesn't add a range Sean Christopherson
2023-09-21 20:33 ` [PATCH 04/13] KVM: WARN if there are danging MMU invalidations at VM destruction Sean Christopherson
2023-09-27  3:16   ` Binbin Wu
2023-09-28 18:11     ` Sean Christopherson
2023-09-21 20:33 ` [PATCH 05/13] KVM: Fix MMU invalidation bookkeeping in guest_memfd Sean Christopherson
2023-09-21 20:33 ` [PATCH 06/13] KVM: Disallow hugepages for incompatible gmem bindings, but let 'em succeed Sean Christopherson
2023-09-22 22:42   ` Michael Roth
2023-09-28 18:31     ` Sean Christopherson
2023-10-02 15:53       ` Michael Roth
2023-10-02 16:49         ` Sean Christopherson
2023-09-21 20:33 ` [PATCH 07/13] KVM: x86/mmu: Track PRIVATE impact on hugepage mappings for all memslots Sean Christopherson
2023-09-27  6:01   ` Binbin Wu [this message]
2023-09-27 14:25     ` Sean Christopherson
2023-09-21 20:33 ` [PATCH 08/13] KVM: x86/mmu: Zap shared-only memslots when private attribute changes Sean Christopherson
2023-09-21 20:33 ` [PATCH 09/13] KVM: Always add relevant ranges to invalidation set when changing attributes Sean Christopherson
2023-09-21 20:33 ` [PATCH 10/13] KVM: x86/mmu: Drop repeated add() of to-be-invalidated range Sean Christopherson
2023-09-21 20:33 ` [PATCH 11/13] KVM: selftests: Refactor private mem conversions to prep for punch_hole test Sean Christopherson
2023-09-21 20:33 ` [PATCH 12/13] KVM: selftests: Add a "pure" PUNCH_HOLE on guest_memfd testcase Sean Christopherson
2023-09-21 20:33 ` [PATCH 13/13] KVM: Rename guest_mem.c to guest_memfd.c Sean Christopherson
2023-09-29  2:22 ` [PATCH 00/13] KVM: guest_memfd fixes Sean Christopherson

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