KVM Archive on lore.kernel.org
 help / color / Atom feed
From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Peter Xu <peterx@redhat.com>
Cc: "James Hogan" <jhogan@kernel.org>,
	"Paul Mackerras" <paulus@ozlabs.org>,
	"Christian Borntraeger" <borntraeger@de.ibm.com>,
	"Janosch Frank" <frankja@linux.ibm.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Marc Zyngier" <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	"Wanpeng Li" <wanpengli@tencent.com>,
	"Philippe Mathieu-Daudé" <f4bug@amsat.org>,
	kvm@vger.kernel.org, "David Hildenbrand" <david@redhat.com>,
	"Joerg Roedel" <joro@8bytes.org>,
	"Cornelia Huck" <cohuck@redhat.com>,
	linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvm-ppc@vger.kernel.org, "Vitaly Kuznetsov" <vkuznets@redhat.com>,
	kvmarm@lists.cs.columbia.edu, "Jim Mattson" <jmattson@google.com>
Subject: Re: [PATCH v4 16/19] KVM: Ensure validity of memslot with respect to kvm_get_dirty_log()
Date: Fri, 7 Feb 2020 10:52:47 -0800
Message-ID: <20200207185247.GJ2401@linux.intel.com> (raw)
In-Reply-To: <20200206220355.GH700495@xz-x1>

On Thu, Feb 06, 2020 at 05:03:55PM -0500, Peter Xu wrote:
> On Tue, Jan 14, 2020 at 10:25:07AM -0800, Sean Christopherson wrote:
> > On Tue, Dec 24, 2019 at 01:19:30PM -0500, Peter Xu wrote:
> > > On Tue, Dec 17, 2019 at 12:40:38PM -0800, Sean Christopherson wrote:
> > > > +int kvm_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log,
> > > > +		      int *is_dirty, struct kvm_memory_slot **memslot)
> > > >  {
> > > >  	struct kvm_memslots *slots;
> > > > -	struct kvm_memory_slot *memslot;
> > > >  	int i, as_id, id;
> > > >  	unsigned long n;
> > > >  	unsigned long any = 0;
> > > >  
> > > > +	*memslot = NULL;
> > > > +	*is_dirty = 0;
> > > > +
> > > >  	as_id = log->slot >> 16;
> > > >  	id = (u16)log->slot;
> > > >  	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_USER_MEM_SLOTS)
> > > >  		return -EINVAL;
> > > >  
> > > >  	slots = __kvm_memslots(kvm, as_id);
> > > > -	memslot = id_to_memslot(slots, id);
> > > > -	if (!memslot->dirty_bitmap)
> > > > +	*memslot = id_to_memslot(slots, id);
> > > > +	if (!(*memslot)->dirty_bitmap)
> > > >  		return -ENOENT;
> > > >  
> > > > -	n = kvm_dirty_bitmap_bytes(memslot);
> > > > +	kvm_arch_sync_dirty_log(kvm, *memslot);
> > > 
> > > Should this line belong to previous patch?
> > 
> > No.
> > 
> > The previous patch, "KVM: Provide common implementation for generic dirty
> > log functions", is consolidating the implementation of dirty log functions
> > for architectures with CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT=y.
> > 
> > This code is being moved from s390's kvm_vm_ioctl_get_dirty_log(), as s390
> > doesn't select KVM_GENERIC_DIRTYLOG_READ_PROTECT.  It's functionally a nop
> > as kvm_arch_sync_dirty_log() is empty for PowerPC, the only other arch that
> > doesn't select KVM_GENERIC_DIRTYLOG_READ_PROTECT.
> > 
> > Arguably, the call to kvm_arch_sync_dirty_log() should be moved in a
> > separate prep patch.  It can't be a follow-on patch as that would swap the
> > ordering of kvm_arch_sync_dirty_log() and kvm_dirty_bitmap_bytes(), etc...
> > 
> > My reasoning for not splitting it to a separate patch is that prior to this
> > patch, the common code and arch specific code are doing separate memslot
> > lookups via id_to_memslot(), i.e. moving the kvm_arch_sync_dirty_log() call
> > would operate on a "different" memslot.   It can't actually be a different
> > memslot because slots_lock is held, it just felt weird.
> > 
> > All that being said, I don't have a strong opinion on moving the call to
> > kvm_arch_sync_dirty_log() in a separate patch; IIRC, I vascillated between
> > the two options when writing the code.  If anyone wants it to be a separate
> > patch I'll happily split it out.
> 
> (Sorry to respond so late)
> 
> I think the confusing part is the subject, where you only mentioned
> the memslot change.  IMHO you can split the change to make it clearer,
> or at least would you mind mention that kvm_arch_sync_dirty_log() move
> in the commit message?  Thanks,

I'll add a few paragraphs to the changelog.  Splitting it out still feels
weird.

  reply index

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-17 20:40 [PATCH v4 00/19] KVM: Dynamically size memslot arrays Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 01/19] KVM: x86: Allocate new rmap and large page tracking when moving memslot Sean Christopherson
2019-12-17 20:48   ` Sean Christopherson
2019-12-17 20:50     ` Sean Christopherson
2019-12-17 21:56   ` Peter Xu
2019-12-17 22:20     ` Sean Christopherson
2019-12-17 22:37       ` Peter Xu
2019-12-17 20:40 ` [PATCH v4 02/19] KVM: Reinstall old memslots if arch preparation fails Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 03/19] KVM: Don't free new memslot if allocation of said memslot fails Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 04/19] KVM: PPC: Move memslot memory allocation into prepare_memory_region() Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 05/19] KVM: x86: Allocate memslot resources during prepare_memory_region() Sean Christopherson
2019-12-17 22:07   ` Peter Xu
2019-12-17 20:40 ` [PATCH v4 06/19] KVM: Drop kvm_arch_create_memslot() Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 07/19] KVM: Explicitly free allocated-but-unused dirty bitmap Sean Christopherson
2019-12-17 22:24   ` Peter Xu
2019-12-17 22:51     ` Sean Christopherson
2019-12-18 16:17       ` Peter Xu
2019-12-17 20:40 ` [PATCH v4 08/19] KVM: Refactor error handling for setting memory region Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 09/19] KVM: Move setting of memslot into helper routine Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 10/19] KVM: Drop "const" attribute from old memslot in commit_memory_region() Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 11/19] KVM: x86: Free arrays for old memslot when moving memslot's base gfn Sean Christopherson
2019-12-17 22:48   ` Peter Xu
2019-12-17 20:40 ` [PATCH v4 12/19] KVM: Move memslot deletion to helper function Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 13/19] KVM: Simplify kvm_free_memslot() and all its descendents Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 14/19] KVM: Clean up local variable usage in __kvm_set_memory_region() Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 15/19] KVM: Provide common implementation for generic dirty log functions Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 16/19] KVM: Ensure validity of memslot with respect to kvm_get_dirty_log() Sean Christopherson
2019-12-24 18:19   ` Peter Xu
2020-01-14 18:25     ` Sean Christopherson
2020-02-06 22:03       ` Peter Xu
2020-02-07 18:52         ` Sean Christopherson [this message]
2019-12-17 20:40 ` [PATCH v4 17/19] KVM: Terminate memslot walks via used_slots Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 18/19] KVM: Dynamically size memslot array based on number of used slots Sean Christopherson
2019-12-17 20:40 ` [PATCH v4 19/19] KVM: selftests: Add test for KVM_SET_USER_MEMORY_REGION Sean Christopherson
2019-12-18 11:29   ` Christian Borntraeger
2019-12-18 11:39   ` Christian Borntraeger
2019-12-18 16:39     ` Sean Christopherson
2020-03-24  9:43       ` Christian Borntraeger
2020-03-24 18:20         ` Sean Christopherson
2019-12-18 11:40 ` [PATCH v4 00/19] KVM: Dynamically size memslot arrays Christian Borntraeger
2019-12-18 18:10 ` Marc Zyngier

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200207185247.GJ2401@linux.intel.com \
    --to=sean.j.christopherson@intel.com \
    --cc=borntraeger@de.ibm.com \
    --cc=cohuck@redhat.com \
    --cc=david@redhat.com \
    --cc=f4bug@amsat.org \
    --cc=frankja@linux.ibm.com \
    --cc=jhogan@kernel.org \
    --cc=jmattson@google.com \
    --cc=joro@8bytes.org \
    --cc=kvm-ppc@vger.kernel.org \
    --cc=kvm@vger.kernel.org \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mips@vger.kernel.org \
    --cc=maz@kernel.org \
    --cc=paulus@ozlabs.org \
    --cc=pbonzini@redhat.com \
    --cc=peterx@redhat.com \
    --cc=vkuznets@redhat.com \
    --cc=wanpengli@tencent.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

KVM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvm/0 kvm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvm kvm/ https://lore.kernel.org/kvm \
		kvm@vger.kernel.org
	public-inbox-index kvm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.kvm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git