by Philippe Mathieu-Daudé

[permalink] [raw]

Subject: Re: [PATCH v3 07/15] KVM: Refactor error handling for setting memory region

On 10/25/19 1:07 AM, Sean Christopherson wrote:
> Replace a big pile o' gotos with returns to make it more obvious what
> error code is being returned, and to prepare for refactoring the
> functional, i.e. post-checks, portion of __kvm_set_memory_region().
>
> Reviewed-by: Janosch Frank <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> virt/kvm/kvm_main.c | 40 ++++++++++++++++++----------------------
> 1 file changed, 18 insertions(+), 22 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index a43902d9036d..e2f47d60f696 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -942,34 +942,33 @@ int __kvm_set_memory_region(struct kvm *kvm,
>
> r = check_memory_region_flags(mem);
> if (r)
> - goto out;
> + return r;
>
> - r = -EINVAL;
> as_id = mem->slot >> 16;
> id = (u16)mem->slot;
>
> /* General sanity checks */
> if (mem->memory_size & (PAGE_SIZE - 1))
> - goto out;
> + return -EINVAL;
> if (mem->guest_phys_addr & (PAGE_SIZE - 1))
> - goto out;
> + return -EINVAL;
> /* We can read the guest memory with __xxx_user() later on. */
> if ((id < KVM_USER_MEM_SLOTS) &&
> ((mem->userspace_addr & (PAGE_SIZE - 1)) ||
> !access_ok((void __user *)(unsigned long)mem->userspace_addr,
> mem->memory_size)))
> - goto out;
> + return -EINVAL;
> if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
> - goto out;
> + return -EINVAL;
> if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> - goto out;
> + return -EINVAL;
>
> slot = id_to_memslot(__kvm_memslots(kvm, as_id), id);
> base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;
> npages = mem->memory_size >> PAGE_SHIFT;
>
> if (npages > KVM_MEM_MAX_NR_PAGES)
> - goto out;
> + return -EINVAL;
>
> new = old = *slot;
>
> @@ -986,20 +985,18 @@ int __kvm_set_memory_region(struct kvm *kvm,
> if ((new.userspace_addr != old.userspace_addr) ||
> (npages != old.npages) ||
> ((new.flags ^ old.flags) & KVM_MEM_READONLY))
> - goto out;
> + return -EINVAL;
>
> if (base_gfn != old.base_gfn)
> change = KVM_MR_MOVE;
> else if (new.flags != old.flags)
> change = KVM_MR_FLAGS_ONLY;
> - else { /* Nothing to change. */
> - r = 0;
> - goto out;
> - }
> + else /* Nothing to change. */
> + return 0;
> }
> } else {
> if (!old.npages)
> - goto out;
> + return -EINVAL;
>
> change = KVM_MR_DELETE;
> new.base_gfn = 0;
> @@ -1008,29 +1005,29 @@ int __kvm_set_memory_region(struct kvm *kvm,
>
> if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
> /* Check for overlaps */
> - r = -EEXIST;
> kvm_for_each_memslot(slot, __kvm_memslots(kvm, as_id)) {
> if (slot->id == id)
> continue;
> if (!((base_gfn + npages <= slot->base_gfn) ||
> (base_gfn >= slot->base_gfn + slot->npages)))
> - goto out;
> + return -EEXIST;
> }
> }
>
> - r = -ENOMEM;
> -
> /* Allocate/free page dirty bitmap as needed */
> if (!(new.flags & KVM_MEM_LOG_DIRTY_PAGES))
> new.dirty_bitmap = NULL;
> else if (!new.dirty_bitmap) {
> - if (kvm_create_dirty_bitmap(&new) < 0)
> - goto out;
> + r = kvm_create_dirty_bitmap(&new);
> + if (r)
> + return r;

Reviewed-by: Philippe Mathieu-Daudé <[email protected]>

> }
>
> slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);
> - if (!slots)
> + if (!slots) {
> + r = -ENOMEM;
> goto out_bitmap;
> + }
> memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots));
>
> if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) {
> @@ -1081,7 +1078,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
> out_bitmap:
> if (new.dirty_bitmap && !old.dirty_bitmap)
> kvm_destroy_dirty_bitmap(&new);
> -out:
> return r;
> }
> EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
>

2019-12-13 20:02:52

by Sean Christopherson

[permalink] [raw]

Subject: Re: [PATCH v3 00/15] KVM: Dynamically size memslot arrays

On Tue, Dec 03, 2019 at 02:14:33PM -0800, Sean Christopherson wrote:
> On Thu, Oct 24, 2019 at 04:07:29PM -0700, Sean Christopherson wrote:
> > The end goal of this series is to dynamically size the memslot array so
> > that KVM allocates memory based on the number of memslots in use, as
> > opposed to unconditionally allocating memory for the maximum number of
> > memslots. On x86, each memslot consumes 88 bytes, and so with 2 address
> > spaces of 512 memslots, each VM consumes ~90k bytes for the memslots.
> > E.g. given a VM that uses a total of 30 memslots, dynamic sizing reduces
> > the memory footprint from 90k to ~2.6k bytes.
> >
> > The changes required to support dynamic sizing are relatively small,
> > e.g. are essentially contained in patches 14/15 and 15/15. Patches 1-13
> > clean up the memslot code, which has gotten quite crusty, especially
> > __kvm_set_memory_region(). The clean up is likely not strictly necessary
> > to switch to dynamic sizing, but I didn't have a remotely reasonable
> > level of confidence in the correctness of the dynamic sizing without first
> > doing the clean up.
> >
> > Christoffer, I added your Tested-by to the patches that I was confident
> > would be fully tested based on the desription of what you tested. Let me
> > know if you disagree with any of 'em.
> >
> > v3:
> > - Fix build errors on PPC and MIPS due to missed params during
> > refactoring [kbuild test robot].
> > - Rename the helpers for update_memslots() and add comments describing
> > the new algorithm and how it interacts with searching [Paolo].
> > - Remove the unnecessary and obnoxious warning regarding memslots being
> > a flexible array [Paolo].
> > - Fix typos in the changelog of patch 09/15 [Christoffer].
> > - Collect tags [Christoffer].
> >
> > v2:
> > - Split "Drop kvm_arch_create_memslot()" into three patches to move
> > minor functional changes to standalone patches [Janosch].
> > - Rebase to latest kvm/queue (f0574a1cea5b, "KVM: x86: fix ...")
> > - Collect an Acked-by and a Reviewed-by
>
> Paolo, do you want me to rebase this to the latest kvm/queue?

Ping.

Applies cleanly on the current kvm/queue and nothing caught fire in
testing (though I only re-tested the series as a whole).