In shadow page table, only leaf SPs may be marked as unsync.
And for non-leaf SPs, we use unsync_children to keep the number
of the unsynced children. In kvm_mmu_sync_root(), sp->unsync
shall always be zero for the root SP, , hence no need to check
it. Instead, a warning inside mmu_sync_children() is added, in
case someone incorrectly used it.
Also, clarify the mmu_need_write_protect(), by moving the warning
into kvm_unsync_page().
Signed-off-by: Yu Zhang <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
Changes in V2:
- warnings added based on Sean's suggestion.
arch/x86/kvm/mmu/mmu.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 86af582..c4797a00cc 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1995,6 +1995,12 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
LIST_HEAD(invalid_list);
bool flush = false;
+ /*
+ * Only 4k SPTEs can directly be made unsync, the parent pages
+ * should never be unsyc'd.
+ */
+ WARN_ON_ONCE(sp->unsync);
+
while (mmu_unsync_walk(parent, &pages)) {
bool protected = false;
@@ -2502,6 +2508,8 @@ int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn)
static void kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
{
+ WARN_ON(sp->role.level != PG_LEVEL_4K);
+
trace_kvm_mmu_unsync_page(sp);
++vcpu->kvm->stat.mmu_unsync;
sp->unsync = 1;
@@ -2524,7 +2532,6 @@ bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
if (sp->unsync)
continue;
- WARN_ON(sp->role.level != PG_LEVEL_4K);
kvm_unsync_page(vcpu, sp);
}
@@ -3406,8 +3413,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu)
* mmu_need_write_protect() describe what could go wrong if this
* requirement isn't satisfied.
*/
- if (!smp_load_acquire(&sp->unsync) &&
- !smp_load_acquire(&sp->unsync_children))
+ if (!smp_load_acquire(&sp->unsync_children))
return;
write_lock(&vcpu->kvm->mmu_lock);
--
1.9.1
On 07/02/21 13:22, Yu Zhang wrote:
> In shadow page table, only leaf SPs may be marked as unsync.
> And for non-leaf SPs, we use unsync_children to keep the number
> of the unsynced children. In kvm_mmu_sync_root(), sp->unsync
> shall always be zero for the root SP, , hence no need to check
> it. Instead, a warning inside mmu_sync_children() is added, in
> case someone incorrectly used it.
>
> Also, clarify the mmu_need_write_protect(), by moving the warning
> into kvm_unsync_page().
>
> Signed-off-by: Yu Zhang <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>
This should really be more of a Co-developed-by, and there are a couple
adjustments that could be made in the commit message. I've queued the
patch and I'll fix it up later.
Paolo
> ---
> Changes in V2:
> - warnings added based on Sean's suggestion.
>
> arch/x86/kvm/mmu/mmu.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 86af582..c4797a00cc 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -1995,6 +1995,12 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
> LIST_HEAD(invalid_list);
> bool flush = false;
>
> + /*
> + * Only 4k SPTEs can directly be made unsync, the parent pages
> + * should never be unsyc'd.
> + */
> + WARN_ON_ONCE(sp->unsync);
> +
> while (mmu_unsync_walk(parent, &pages)) {
> bool protected = false;
>
> @@ -2502,6 +2508,8 @@ int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn)
>
> static void kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
> {
> + WARN_ON(sp->role.level != PG_LEVEL_4K);
> +
> trace_kvm_mmu_unsync_page(sp);
> ++vcpu->kvm->stat.mmu_unsync;
> sp->unsync = 1;
> @@ -2524,7 +2532,6 @@ bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
> if (sp->unsync)
> continue;
>
> - WARN_ON(sp->role.level != PG_LEVEL_4K);
> kvm_unsync_page(vcpu, sp);
> }
>
> @@ -3406,8 +3413,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu)
> * mmu_need_write_protect() describe what could go wrong if this
> * requirement isn't satisfied.
> */
> - if (!smp_load_acquire(&sp->unsync) &&
> - !smp_load_acquire(&sp->unsync_children))
> + if (!smp_load_acquire(&sp->unsync_children))
> return;
>
> write_lock(&vcpu->kvm->mmu_lock);
>
On Mon, Feb 08, 2021 at 12:36:57PM +0100, Paolo Bonzini wrote:
> On 07/02/21 13:22, Yu Zhang wrote:
> > In shadow page table, only leaf SPs may be marked as unsync.
> > And for non-leaf SPs, we use unsync_children to keep the number
> > of the unsynced children. In kvm_mmu_sync_root(), sp->unsync
> > shall always be zero for the root SP, , hence no need to check
> > it. Instead, a warning inside mmu_sync_children() is added, in
> > case someone incorrectly used it.
> >
> > Also, clarify the mmu_need_write_protect(), by moving the warning
> > into kvm_unsync_page().
> >
> > Signed-off-by: Yu Zhang <[email protected]>
> > Signed-off-by: Sean Christopherson <[email protected]>
>
> This should really be more of a Co-developed-by, and there are a couple
> adjustments that could be made in the commit message. I've queued the patch
> and I'll fix it up later.
Indeed. Thanks for the remind, and I'll pay attention in the future. :)
B.R.
Yu
>
> Paolo
>
> > ---
> > Changes in V2:
> > - warnings added based on Sean's suggestion.
> >
> > arch/x86/kvm/mmu/mmu.c | 12 +++++++++---
> > 1 file changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 86af582..c4797a00cc 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -1995,6 +1995,12 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
> > LIST_HEAD(invalid_list);
> > bool flush = false;
> > + /*
> > + * Only 4k SPTEs can directly be made unsync, the parent pages
> > + * should never be unsyc'd.
> > + */
> > + WARN_ON_ONCE(sp->unsync);
> > +
> > while (mmu_unsync_walk(parent, &pages)) {
> > bool protected = false;
> > @@ -2502,6 +2508,8 @@ int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn)
> > static void kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
> > {
> > + WARN_ON(sp->role.level != PG_LEVEL_4K);
> > +
> > trace_kvm_mmu_unsync_page(sp);
> > ++vcpu->kvm->stat.mmu_unsync;
> > sp->unsync = 1;
> > @@ -2524,7 +2532,6 @@ bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
> > if (sp->unsync)
> > continue;
> > - WARN_ON(sp->role.level != PG_LEVEL_4K);
> > kvm_unsync_page(vcpu, sp);
> > }
> > @@ -3406,8 +3413,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu)
> > * mmu_need_write_protect() describe what could go wrong if this
> > * requirement isn't satisfied.
> > */
> > - if (!smp_load_acquire(&sp->unsync) &&
> > - !smp_load_acquire(&sp->unsync_children))
> > + if (!smp_load_acquire(&sp->unsync_children))
> > return;
> > write_lock(&vcpu->kvm->mmu_lock);
> >
>
On 08/02/21 14:49, Yu Zhang wrote:
> On Mon, Feb 08, 2021 at 12:36:57PM +0100, Paolo Bonzini wrote:
>> On 07/02/21 13:22, Yu Zhang wrote:
>>> In shadow page table, only leaf SPs may be marked as unsync.
>>> And for non-leaf SPs, we use unsync_children to keep the number
>>> of the unsynced children. In kvm_mmu_sync_root(), sp->unsync
>>> shall always be zero for the root SP, , hence no need to check
>>> it. Instead, a warning inside mmu_sync_children() is added, in
>>> case someone incorrectly used it.
>>>
>>> Also, clarify the mmu_need_write_protect(), by moving the warning
>>> into kvm_unsync_page().
>>>
>>> Signed-off-by: Yu Zhang <[email protected]>
>>> Signed-off-by: Sean Christopherson <[email protected]>
>>
>> This should really be more of a Co-developed-by, and there are a couple
>> adjustments that could be made in the commit message. I've queued the patch
>> and I'll fix it up later.
>
> Indeed. Thanks for the remind, and I'll pay attention in the future. :)
Also:
arch/x86/kvm/mmu/mmu.c: In function ‘mmu_sync_children’:
arch/x86/kvm/mmu/mmu.c:2002:17: error: ‘sp’ is used uninitialized in
this function [-Werror=uninitialized]
WARN_ON_ONCE(sp->unsync);
so how was this tested?
Paolo
On Mon, Feb 08, 2021 at 05:47:22PM +0100, Paolo Bonzini wrote:
> On 08/02/21 14:49, Yu Zhang wrote:
> > On Mon, Feb 08, 2021 at 12:36:57PM +0100, Paolo Bonzini wrote:
> > > On 07/02/21 13:22, Yu Zhang wrote:
> > > > In shadow page table, only leaf SPs may be marked as unsync.
> > > > And for non-leaf SPs, we use unsync_children to keep the number
> > > > of the unsynced children. In kvm_mmu_sync_root(), sp->unsync
> > > > shall always be zero for the root SP, , hence no need to check
> > > > it. Instead, a warning inside mmu_sync_children() is added, in
> > > > case someone incorrectly used it.
> > > >
> > > > Also, clarify the mmu_need_write_protect(), by moving the warning
> > > > into kvm_unsync_page().
> > > >
> > > > Signed-off-by: Yu Zhang <[email protected]>
> > > > Signed-off-by: Sean Christopherson <[email protected]>
> > >
> > > This should really be more of a Co-developed-by, and there are a couple
> > > adjustments that could be made in the commit message. I've queued the patch
> > > and I'll fix it up later.
> >
> > Indeed. Thanks for the remind, and I'll pay attention in the future. :)
>
> Also:
>
> arch/x86/kvm/mmu/mmu.c: In function ‘mmu_sync_children’:
> arch/x86/kvm/mmu/mmu.c:2002:17: error: ‘sp’ is used uninitialized in this
> function [-Werror=uninitialized]
> WARN_ON_ONCE(sp->unsync);
Oops. This is wrong. Should be WARN_ON_ONCE(parent->unsync);
>
> so how was this tested?
>
I ran access test in kvm-unit-test for previous version, which hasn't
this code(also in my local repo "enable_ept" was explicitly set to
0 in order to test the shadow mode). But I did not test this one. I'm
truely sorry for the negligence - even trying to compile should make
this happen!
Should we submit another version? Any suggestions on the test cases?
Thanks
Yu
> Paolo
>
On 09/02/21 04:33, Yu Zhang wrote:
> On Mon, Feb 08, 2021 at 05:47:22PM +0100, Paolo Bonzini wrote:
>> On 08/02/21 14:49, Yu Zhang wrote:
>>> On Mon, Feb 08, 2021 at 12:36:57PM +0100, Paolo Bonzini wrote:
>>>> On 07/02/21 13:22, Yu Zhang wrote:
>>>>> In shadow page table, only leaf SPs may be marked as unsync.
>>>>> And for non-leaf SPs, we use unsync_children to keep the number
>>>>> of the unsynced children. In kvm_mmu_sync_root(), sp->unsync
>>>>> shall always be zero for the root SP, , hence no need to check
>>>>> it. Instead, a warning inside mmu_sync_children() is added, in
>>>>> case someone incorrectly used it.
>>>>>
>>>>> Also, clarify the mmu_need_write_protect(), by moving the warning
>>>>> into kvm_unsync_page().
>>>>>
>>>>> Signed-off-by: Yu Zhang <[email protected]>
>>>>> Signed-off-by: Sean Christopherson <[email protected]>
>>>>
>>>> This should really be more of a Co-developed-by, and there are a couple
>>>> adjustments that could be made in the commit message. I've queued the patch
>>>> and I'll fix it up later.
>>>
>>> Indeed. Thanks for the remind, and I'll pay attention in the future. :)
>>
>> Also:
>>
>> arch/x86/kvm/mmu/mmu.c: In function ‘mmu_sync_children’:
>> arch/x86/kvm/mmu/mmu.c:2002:17: error: ‘sp’ is used uninitialized in this
>> function [-Werror=uninitialized]
>> WARN_ON_ONCE(sp->unsync);
>
> Oops. This is wrong. Should be WARN_ON_ONCE(parent->unsync);
>
>>
>> so how was this tested?
>>
>
> I ran access test in kvm-unit-test for previous version, which hasn't
> this code(also in my local repo "enable_ept" was explicitly set to
> 0 in order to test the shadow mode). But I did not test this one. I'm
> truely sorry for the negligence - even trying to compile should make
> this happen!
>
> Should we submit another version? Any suggestions on the test cases?
Yes, please send v3.
The commit message can be:
In shadow page table, only leaf SPs may be marked as unsync; instead,
for non-leaf SPs, we store the number of unsynced children in
unsync_children. Therefore, in kvm_mmu_sync_root(), sp->unsync
shall always be zero for the root SP and there is no need to check
it. Remove the check, and add a warning inside mmu_sync_children() to
assert that the flags are used properly.
While at it, move the warning from mmu_need_write_protect() to
kvm_unsync_page().
Paolo
On Tue, Feb 09, 2021 at 08:46:42AM +0100, Paolo Bonzini wrote:
> On 09/02/21 04:33, Yu Zhang wrote:
> > On Mon, Feb 08, 2021 at 05:47:22PM +0100, Paolo Bonzini wrote:
> > > On 08/02/21 14:49, Yu Zhang wrote:
> > > > On Mon, Feb 08, 2021 at 12:36:57PM +0100, Paolo Bonzini wrote:
> > > > > On 07/02/21 13:22, Yu Zhang wrote:
> > > > > > In shadow page table, only leaf SPs may be marked as unsync.
> > > > > > And for non-leaf SPs, we use unsync_children to keep the number
> > > > > > of the unsynced children. In kvm_mmu_sync_root(), sp->unsync
> > > > > > shall always be zero for the root SP, , hence no need to check
> > > > > > it. Instead, a warning inside mmu_sync_children() is added, in
> > > > > > case someone incorrectly used it.
> > > > > >
> > > > > > Also, clarify the mmu_need_write_protect(), by moving the warning
> > > > > > into kvm_unsync_page().
> > > > > >
> > > > > > Signed-off-by: Yu Zhang <[email protected]>
> > > > > > Signed-off-by: Sean Christopherson <[email protected]>
> > > > >
> > > > > This should really be more of a Co-developed-by, and there are a couple
> > > > > adjustments that could be made in the commit message. I've queued the patch
> > > > > and I'll fix it up later.
> > > >
> > > > Indeed. Thanks for the remind, and I'll pay attention in the future. :)
> > >
> > > Also:
> > >
> > > arch/x86/kvm/mmu/mmu.c: In function ‘mmu_sync_children’:
> > > arch/x86/kvm/mmu/mmu.c:2002:17: error: ‘sp’ is used uninitialized in this
> > > function [-Werror=uninitialized]
> > > WARN_ON_ONCE(sp->unsync);
> >
> > Oops. This is wrong. Should be WARN_ON_ONCE(parent->unsync);
> >
> > >
> > > so how was this tested?
> > >
> >
> > I ran access test in kvm-unit-test for previous version, which hasn't
> > this code(also in my local repo "enable_ept" was explicitly set to
> > 0 in order to test the shadow mode). But I did not test this one. I'm
> > truely sorry for the negligence - even trying to compile should make
> > this happen!
> >
> > Should we submit another version? Any suggestions on the test cases?
>
> Yes, please send v3.
>
> The commit message can be:
>
> In shadow page table, only leaf SPs may be marked as unsync; instead, for
> non-leaf SPs, we store the number of unsynced children in unsync_children.
> Therefore, in kvm_mmu_sync_root(), sp->unsync
> shall always be zero for the root SP and there is no need to check
> it. Remove the check, and add a warning inside mmu_sync_children() to
> assert that the flags are used properly.
>
> While at it, move the warning from mmu_need_write_protect() to
> kvm_unsync_page().
Thanks Paolo. Will send out v3.
BTW, I just realized that mmu_sync_children() was not triggered by
kvm-unit-test(the access.flat case), so I ran another test by running
a regular VM using shadow, in which I witnessed the synchronization.
B.R.
Yu
>
> Paolo
>