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From: Peter Xu <peterx@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
	"Paul Mackerras" <paulus@ozlabs.org>,
	"Christian Borntraeger" <borntraeger@de.ibm.com>,
	"Janosch Frank" <frankja@linux.ibm.com>,
	"David Hildenbrand" <david@redhat.com>,
	"Cornelia Huck" <cohuck@redhat.com>,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>,
	"Wanpeng Li" <wanpengli@tencent.com>,
	"Jim Mattson" <jmattson@google.com>,
	"Joerg Roedel" <joro@8bytes.org>, "Marc Zyngier" <maz@kernel.org>,
	"James Morse" <james.morse@arm.com>,
	"Julien Thierry" <julien.thierry.kdev@gmail.com>,
	"Suzuki K Poulose" <suzuki.poulose@arm.com>,
	linux-mips@vger.kernel.org, kvm@vger.kernel.org,
	kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
	"Christoffer Dall" <christoffer.dall@arm.com>,
	"Philippe Mathieu-Daudé" <f4bug@amsat.org>
Subject: Re: [PATCH v5 18/19] KVM: Dynamically size memslot array based on number of used slots
Date: Thu, 6 Feb 2020 17:12:08 -0500
Message-ID: <20200206221208.GI700495@xz-x1> (raw)
In-Reply-To: <20200121223157.15263-19-sean.j.christopherson@intel.com>

On Tue, Jan 21, 2020 at 02:31:56PM -0800, Sean Christopherson wrote:
> Now that the memslot logic doesn't assume memslots are always non-NULL,
> dynamically size the array of memslots instead of unconditionally
> allocating memory for the maximum number of memslots.
> 
> Note, because a to-be-deleted memslot must first be invalidated, the
> array size cannot be immediately reduced when deleting a memslot.
> However, consecutive deletions will realize the memory savings, i.e.
> a second deletion will trim the entry.
> 
> Tested-by: Christoffer Dall <christoffer.dall@arm.com>
> Tested-by: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  include/linux/kvm_host.h |  2 +-
>  virt/kvm/kvm_main.c      | 31 ++++++++++++++++++++++++++++---
>  2 files changed, 29 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 60ddfdb69378..8bb6fb127387 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -431,11 +431,11 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu)
>   */
>  struct kvm_memslots {
>  	u64 generation;
> -	struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
>  	/* The mapping table from slot id to the index in memslots[]. */
>  	short id_to_index[KVM_MEM_SLOTS_NUM];
>  	atomic_t lru_slot;
>  	int used_slots;
> +	struct kvm_memory_slot memslots[];

This patch is tested so I believe this works, however normally I need
to do similar thing with [0] otherwise gcc might complaint.  Is there
any trick behind to make this work?  Or is that because of different
gcc versions?

>  };
>  
>  struct kvm {
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 9b614cf2ca20..ed392ce64e59 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -565,7 +565,7 @@ static struct kvm_memslots *kvm_alloc_memslots(void)
>  		return NULL;
>  
>  	for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
> -		slots->id_to_index[i] = slots->memslots[i].id = -1;
> +		slots->id_to_index[i] = -1;
>  
>  	return slots;
>  }
> @@ -1077,6 +1077,32 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
>  	return old_memslots;
>  }
>  
> +/*
> + * Note, at a minimum, the current number of used slots must be allocated, even
> + * when deleting a memslot, as we need a complete duplicate of the memslots for
> + * use when invalidating a memslot prior to deleting/moving the memslot.
> + */
> +static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
> +					     enum kvm_mr_change change)
> +{
> +	struct kvm_memslots *slots;
> +	size_t old_size, new_size;
> +
> +	old_size = sizeof(struct kvm_memslots) +
> +		   (sizeof(struct kvm_memory_slot) * old->used_slots);
> +
> +	if (change == KVM_MR_CREATE)
> +		new_size = old_size + sizeof(struct kvm_memory_slot);
> +	else
> +		new_size = old_size;
> +
> +	slots = kvzalloc(new_size, GFP_KERNEL_ACCOUNT);
> +	if (likely(slots))
> +		memcpy(slots, old, old_size);

(Maybe directly copy into it?)

> +
> +	return slots;
> +}
> +
>  static int kvm_set_memslot(struct kvm *kvm,
>  			   const struct kvm_userspace_memory_region *mem,
>  			   struct kvm_memory_slot *old,
> @@ -1087,10 +1113,9 @@ static int kvm_set_memslot(struct kvm *kvm,
>  	struct kvm_memslots *slots;
>  	int r;
>  
> -	slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);
> +	slots = kvm_dup_memslots(__kvm_memslots(kvm, as_id), change);
>  	if (!slots)
>  		return -ENOMEM;
> -	memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots));
>  
>  	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
>  		/*
> -- 
> 2.24.1
> 

-- 
Peter Xu


  reply index

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-21 22:31 [PATCH v5 00/19] KVM: Dynamically size memslot arrays Sean Christopherson
2020-01-21 22:31 ` [PATCH v5 01/19] KVM: x86: Allocate new rmap and large page tracking when moving memslot Sean Christopherson
2020-02-05 21:49   ` Peter Xu
2020-02-05 23:55     ` Sean Christopherson
2020-02-06  2:00       ` Peter Xu
2020-02-06  2:17         ` Sean Christopherson
2020-02-06  2:58           ` Peter Xu
2020-02-06  5:05             ` Sean Christopherson
2020-01-21 22:31 ` [PATCH v5 02/19] KVM: Reinstall old memslots if arch preparation fails Sean Christopherson
2020-02-05 22:08   ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 03/19] KVM: Don't free new memslot if allocation of said memslot fails Sean Christopherson
2020-02-05 22:28   ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 04/19] KVM: PPC: Move memslot memory allocation into prepare_memory_region() Sean Christopherson
2020-02-05 22:41   ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 05/19] KVM: x86: Allocate memslot resources during prepare_memory_region() Sean Christopherson
2020-01-21 22:31 ` [PATCH v5 06/19] KVM: Drop kvm_arch_create_memslot() Sean Christopherson
2020-02-05 22:45   ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 07/19] KVM: Explicitly free allocated-but-unused dirty bitmap Sean Christopherson
2020-01-21 22:31 ` [PATCH v5 08/19] KVM: Refactor error handling for setting memory region Sean Christopherson
2020-02-05 22:48   ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 09/19] KVM: Move setting of memslot into helper routine Sean Christopherson
2020-02-06 16:26   ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 10/19] KVM: Drop "const" attribute from old memslot in commit_memory_region() Sean Christopherson
2020-02-06 16:26   ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 11/19] KVM: x86: Free arrays for old memslot when moving memslot's base gfn Sean Christopherson
2020-01-21 22:31 ` [PATCH v5 12/19] KVM: Move memslot deletion to helper function Sean Christopherson
2020-02-06 16:14   ` Peter Xu
2020-02-06 16:28     ` Sean Christopherson
2020-02-06 16:51       ` Peter Xu
2020-02-07 17:59         ` Sean Christopherson
2020-02-07 18:07           ` Sean Christopherson
2020-02-07 18:17           ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 13/19] KVM: Simplify kvm_free_memslot() and all its descendents Sean Christopherson
2020-02-06 16:29   ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 14/19] KVM: Clean up local variable usage in __kvm_set_memory_region() Sean Christopherson
2020-02-06 19:06   ` Peter Xu
2020-02-06 19:22     ` Sean Christopherson
2020-02-06 19:36       ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 15/19] KVM: Provide common implementation for generic dirty log functions Sean Christopherson
2020-02-06 20:02   ` Peter Xu
2020-02-06 21:21     ` Sean Christopherson
2020-02-06 21:41       ` Peter Xu
2020-02-07 19:45         ` Sean Christopherson
2020-02-08  0:18           ` Peter Xu
2020-02-08  0:42             ` Sean Christopherson
2020-02-08  0:53               ` Peter Xu
2020-02-08  1:29                 ` Sean Christopherson
2020-02-17 15:39                   ` Vitaly Kuznetsov
2020-02-18 17:10                     ` Sean Christopherson
2020-02-17 15:35           ` Vitaly Kuznetsov
2020-02-06 21:24   ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 16/19] KVM: Ensure validity of memslot with respect to kvm_get_dirty_log() Sean Christopherson
2020-01-21 22:31 ` [PATCH v5 17/19] KVM: Terminate memslot walks via used_slots Sean Christopherson
2020-02-06 21:09   ` Peter Xu
2020-02-07 18:33     ` Sean Christopherson
2020-02-07 20:39       ` Peter Xu
2020-02-07 21:10         ` Sean Christopherson
2020-02-07 21:46           ` Peter Xu
2020-02-07 22:03             ` Sean Christopherson
2020-02-07 22:24               ` Peter Xu
2020-01-21 22:31 ` [PATCH v5 18/19] KVM: Dynamically size memslot array based on number of used slots Sean Christopherson
2020-02-06 22:12   ` Peter Xu [this message]
2020-02-07 15:38     ` Sean Christopherson
2020-02-07 16:05       ` Peter Xu
2020-02-07 16:15         ` Sean Christopherson
2020-02-07 16:37           ` Peter Xu
2020-02-07 16:47             ` Sean Christopherson
2020-01-21 22:31 ` [PATCH v5 19/19] KVM: selftests: Add test for KVM_SET_USER_MEMORY_REGION Sean Christopherson
2020-02-06 22:30   ` Peter Xu
2020-02-06 23:11     ` Sean Christopherson

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