From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Peter Xu <peterx@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Christophe de Dinechin <dinechin@redhat.com>,
"Michael S . Tsirkin" <mst@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Yan Zhao <yan.y.zhao@intel.com>,
Alex Williamson <alex.williamson@redhat.com>,
Jason Wang <jasowang@redhat.com>,
Kevin Kevin <kevin.tian@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: [PATCH v3 09/21] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]
Date: Fri, 31 Jan 2020 12:36:22 -0800 [thread overview]
Message-ID: <20200131203622.GF18946@linux.intel.com> (raw)
In-Reply-To: <20200131202824.GA7063@xz-x1>
On Fri, Jan 31, 2020 at 03:28:24PM -0500, Peter Xu wrote:
> On Fri, Jan 31, 2020 at 11:33:01AM -0800, Sean Christopherson wrote:
> > For the same reason we don't take mmap_sem, it gains us nothing, i.e. KVM
> > still has to use copy_{to,from}_user().
> >
> > In the proposed __x86_set_memory_region() refactor, vmx_set_tss_addr()
> > would be provided the hva of the memory region. Since slots_lock and SRCU
> > only protect gfn->hva, why would KVM take slots_lock since it already has
> > the hva?
>
> OK so you're suggesting to unlock the lock earlier to not cover
> init_rmode_tss() rather than dropping the whole lock... Yes it looks
> good to me. I think that's the major confusion I got.
Ya. And I missed where the -EEXIST was coming from. I think we're on the
same page.
> > Returning -EEXIST is an ABI change, e.g. userspace can currently call
> > KVM_SET_TSS_ADDR any number of times, it just needs to ensure proper
> > serialization between calls.
> >
> > If you want to change the ABI, then submit a patch to do exactly that.
> > But don't bury an ABI change under the pretense that it's a bug fix.
>
> Could you explain what do you mean by "ABI change"?
>
> I was talking about the original code, not after applying the
> patchset. To be explicit, I mean [a] below:
>
> int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size,
> unsigned long *uaddr)
> {
> int i, r;
> unsigned long hva;
> struct kvm_memslots *slots = kvm_memslots(kvm);
> struct kvm_memory_slot *slot, old;
>
> /* Called with kvm->slots_lock held. */
> if (WARN_ON(id >= KVM_MEM_SLOTS_NUM))
> return -EINVAL;
>
> slot = id_to_memslot(slots, id);
> if (size) {
> if (slot->npages)
> return -EEXIST; <------------------------ [a]
> }
> ...
> }
Doh, I completely forgot that the second __x86_set_memory_region() would
fail. Sorry :-(
> > > Yes, but as I mentioned, I don't think it's an issue to be considered
> > > by KVM, otherwise we should have the same issue all over the places
> > > when we fetch the cached userspace_addr from any user slots.
> >
> > Huh? Of course it's an issue that needs to be considered by KVM, e.g.
> > kvm_{read,write}_guest_cached() aren't using __copy_{to,}from_user() for
> > giggles.
>
> The cache is for the GPA->HVA translation (struct gfn_to_hva_cache),
> we still use __copy_{to,}from_user() upon the HVAs, no?
I'm still lost on this one. I'm pretty sure I'm incorrectly interpreting:
I don't think it's an issue to be considered by KVM, otherwise we should
have the same issue all over the places when we fetch the cached
userspace_addr from any user slots.
What is the issue to which you are referring?
next prev parent reply other threads:[~2020-01-31 20:36 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-09 14:57 [PATCH v3 00/21] KVM: Dirty ring interface Peter Xu
2020-01-09 14:57 ` [PATCH v3 01/21] vfio: introduce vfio_iova_rw to read/write a range of IOVAs Peter Xu
2020-01-09 14:57 ` [PATCH v3 02/21] drm/i915/gvt: subsitute kvm_read/write_guest with vfio_iova_rw Peter Xu
2020-01-09 14:57 ` [PATCH v3 03/21] KVM: Remove kvm_read_guest_atomic() Peter Xu
2020-01-09 14:57 ` [PATCH v3 04/21] KVM: Add build-time error check on kvm_run size Peter Xu
2020-01-09 14:57 ` [PATCH v3 05/21] KVM: X86: Change parameter for fast_page_fault tracepoint Peter Xu
2020-01-09 14:57 ` [PATCH v3 06/21] KVM: X86: Don't take srcu lock in init_rmode_identity_map() Peter Xu
2020-01-09 14:57 ` [PATCH v3 07/21] KVM: Cache as_id in kvm_memory_slot Peter Xu
2020-01-09 14:57 ` [PATCH v3 08/21] KVM: X86: Drop x86_set_memory_region() Peter Xu
2020-01-09 14:57 ` [PATCH v3 09/21] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR] Peter Xu
2020-01-19 9:01 ` Paolo Bonzini
2020-01-20 6:45 ` Peter Xu
2020-01-21 15:56 ` Sean Christopherson
2020-01-21 16:14 ` Paolo Bonzini
2020-01-28 5:50 ` Peter Xu
2020-01-28 18:24 ` Sean Christopherson
2020-01-31 15:08 ` Peter Xu
2020-01-31 19:33 ` Sean Christopherson
2020-01-31 20:28 ` Peter Xu
2020-01-31 20:36 ` Sean Christopherson [this message]
2020-01-31 20:55 ` Peter Xu
2020-01-31 21:29 ` Sean Christopherson
2020-01-31 22:16 ` Peter Xu
2020-01-31 22:20 ` Sean Christopherson
2020-01-09 14:57 ` [PATCH v3 10/21] KVM: Pass in kvm pointer into mark_page_dirty_in_slot() Peter Xu
2020-01-09 14:57 ` [PATCH v3 11/21] KVM: Move running VCPU from ARM to common code Peter Xu
2020-01-09 14:57 ` [PATCH v3 12/21] KVM: X86: Implement ring-based dirty memory tracking Peter Xu
2020-01-09 16:29 ` Michael S. Tsirkin
2020-01-09 16:56 ` Alex Williamson
2020-01-09 19:21 ` Peter Xu
2020-01-09 19:36 ` Michael S. Tsirkin
2020-01-09 19:15 ` Peter Xu
2020-01-09 19:35 ` Michael S. Tsirkin
2020-01-09 20:19 ` Peter Xu
2020-01-09 22:18 ` Michael S. Tsirkin
2020-01-10 15:29 ` Peter Xu
2020-01-12 6:24 ` Michael S. Tsirkin
2020-01-14 20:01 ` Peter Xu
2020-01-15 6:50 ` Michael S. Tsirkin
2020-01-15 15:20 ` Peter Xu
2020-01-19 9:09 ` Paolo Bonzini
2020-01-19 10:12 ` Michael S. Tsirkin
2020-01-20 7:29 ` Peter Xu
2020-01-20 7:47 ` Michael S. Tsirkin
2020-01-21 8:29 ` Peter Xu
2020-01-21 10:25 ` Paolo Bonzini
2020-01-21 10:24 ` Paolo Bonzini
2020-01-11 4:49 ` kbuild test robot
2020-01-11 23:19 ` kbuild test robot
2020-01-15 6:47 ` Michael S. Tsirkin
2020-01-15 15:27 ` Peter Xu
2020-01-16 8:38 ` Michael S. Tsirkin
2020-01-16 16:27 ` Peter Xu
2020-01-17 9:50 ` Michael S. Tsirkin
2020-01-20 6:48 ` Peter Xu
2020-01-09 14:57 ` [PATCH v3 13/21] KVM: Make dirty ring exclusive to dirty bitmap log Peter Xu
2020-01-09 14:57 ` [PATCH v3 14/21] KVM: Don't allocate dirty bitmap if dirty ring is enabled Peter Xu
2020-01-09 16:41 ` Peter Xu
2020-01-09 14:57 ` [PATCH v3 15/21] KVM: selftests: Always clear dirty bitmap after iteration Peter Xu
2020-01-09 14:57 ` [PATCH v3 16/21] KVM: selftests: Sync uapi/linux/kvm.h to tools/ Peter Xu
2020-01-09 14:57 ` [PATCH v3 17/21] KVM: selftests: Use a single binary for dirty/clear log test Peter Xu
2020-01-09 14:57 ` [PATCH v3 18/21] KVM: selftests: Introduce after_vcpu_run hook for dirty " Peter Xu
2020-01-09 14:57 ` [PATCH v3 19/21] KVM: selftests: Add dirty ring buffer test Peter Xu
2020-01-09 14:57 ` [PATCH v3 20/21] KVM: selftests: Let dirty_log_test async for dirty ring test Peter Xu
2020-01-09 14:57 ` [PATCH v3 21/21] KVM: selftests: Add "-c" parameter to dirty log test Peter Xu
2020-01-09 15:59 ` [PATCH v3 00/21] KVM: Dirty ring interface Michael S. Tsirkin
2020-01-09 16:17 ` Peter Xu
2020-01-09 16:40 ` Michael S. Tsirkin
2020-01-09 17:08 ` Peter Xu
2020-01-09 19:08 ` Michael S. Tsirkin
2020-01-09 19:39 ` Peter Xu
2020-01-09 20:42 ` Paolo Bonzini
2020-01-09 22:28 ` Michael S. Tsirkin
2020-01-10 15:10 ` Peter Xu
2020-01-09 16:47 ` Alex Williamson
2020-01-09 17:58 ` Peter Xu
2020-01-09 19:13 ` Michael S. Tsirkin
2020-01-09 19:23 ` Peter Xu
2020-01-09 19:37 ` Michael S. Tsirkin
2020-01-09 20:51 ` Paolo Bonzini
2020-01-09 22:21 ` Michael S. Tsirkin
2020-01-19 9:11 ` Paolo Bonzini
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