* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-14 16:56 [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated Tony Krowiak
@ 2020-12-14 17:07 ` Greg KH
2020-12-14 19:39 ` Tony Krowiak
2020-12-15 10:57 ` Halil Pasic
` (2 subsequent siblings)
3 siblings, 1 reply; 15+ messages in thread
From: Greg KH @ 2020-12-14 17:07 UTC (permalink / raw)
To: Tony Krowiak
Cc: linux-s390, linux-kernel, kvm, stable, sashal, borntraeger,
cohuck, kwankhede, pbonzini, alex.williamson, pasic
On Mon, Dec 14, 2020 at 11:56:17AM -0500, Tony Krowiak wrote:
> The vfio_ap device driver registers a group notifier with VFIO when the
> file descriptor for a VFIO mediated device for a KVM guest is opened to
> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> event). When the KVM pointer is set, the vfio_ap driver takes the
> following actions:
> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
> of the mediated device.
> 2. Calls the kvm_get_kvm() function to increment its reference counter.
> 3. Sets the function pointer to the function that handles interception of
> the instruction that enables/disables interrupt processing.
> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
> the guest.
>
> In order to avoid memory leaks, when the notifier is called to receive
> notification that the KVM pointer has been set to NULL, the vfio_ap device
> driver should reverse the actions taken when the KVM pointer was set.
>
> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
> 1 file changed, 20 insertions(+), 9 deletions(-)
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.
</formletter>
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-14 17:07 ` Greg KH
@ 2020-12-14 19:39 ` Tony Krowiak
2020-12-14 19:43 ` Greg KH
0 siblings, 1 reply; 15+ messages in thread
From: Tony Krowiak @ 2020-12-14 19:39 UTC (permalink / raw)
To: Greg KH
Cc: linux-s390, linux-kernel, kvm, stable, sashal, borntraeger,
cohuck, kwankhede, pbonzini, alex.williamson, pasic
On 12/14/20 12:07 PM, Greg KH wrote:
> On Mon, Dec 14, 2020 at 11:56:17AM -0500, Tony Krowiak wrote:
>> The vfio_ap device driver registers a group notifier with VFIO when the
>> file descriptor for a VFIO mediated device for a KVM guest is opened to
>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
>> event). When the KVM pointer is set, the vfio_ap driver takes the
>> following actions:
>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
>> of the mediated device.
>> 2. Calls the kvm_get_kvm() function to increment its reference counter.
>> 3. Sets the function pointer to the function that handles interception of
>> the instruction that enables/disables interrupt processing.
>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
>> the guest.
>>
>> In order to avoid memory leaks, when the notifier is called to receive
>> notification that the KVM pointer has been set to NULL, the vfio_ap device
>> driver should reverse the actions taken when the KVM pointer was set.
>>
>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>> ---
>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
>> 1 file changed, 20 insertions(+), 9 deletions(-)
> <formletter>
>
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree. Please read:
> https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> for how to do this properly.
>
> </formletter>
I read the document on the correct way to submit patches for inclusion in
the stable kernel. I apologize for my ignorance, but I don't see the
problem. Can you help me out here? Does a patch that fixes a memory leak
not qualify or is it something else?
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-14 19:39 ` Tony Krowiak
@ 2020-12-14 19:43 ` Greg KH
2020-12-14 19:48 ` Tony Krowiak
0 siblings, 1 reply; 15+ messages in thread
From: Greg KH @ 2020-12-14 19:43 UTC (permalink / raw)
To: Tony Krowiak
Cc: linux-s390, linux-kernel, kvm, stable, sashal, borntraeger,
cohuck, kwankhede, pbonzini, alex.williamson, pasic
On Mon, Dec 14, 2020 at 02:39:17PM -0500, Tony Krowiak wrote:
>
>
> On 12/14/20 12:07 PM, Greg KH wrote:
> > On Mon, Dec 14, 2020 at 11:56:17AM -0500, Tony Krowiak wrote:
> > > The vfio_ap device driver registers a group notifier with VFIO when the
> > > file descriptor for a VFIO mediated device for a KVM guest is opened to
> > > receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> > > event). When the KVM pointer is set, the vfio_ap driver takes the
> > > following actions:
> > > 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
> > > of the mediated device.
> > > 2. Calls the kvm_get_kvm() function to increment its reference counter.
> > > 3. Sets the function pointer to the function that handles interception of
> > > the instruction that enables/disables interrupt processing.
> > > 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
> > > the guest.
> > >
> > > In order to avoid memory leaks, when the notifier is called to receive
> > > notification that the KVM pointer has been set to NULL, the vfio_ap device
> > > driver should reverse the actions taken when the KVM pointer was set.
> > >
> > > Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> > > Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> > > ---
> > > drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
> > > 1 file changed, 20 insertions(+), 9 deletions(-)
> > <formletter>
> >
> > This is not the correct way to submit patches for inclusion in the
> > stable kernel tree. Please read:
> > https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> > for how to do this properly.
> >
> > </formletter>
>
> I read the document on the correct way to submit patches for inclusion in
> the stable kernel. I apologize for my ignorance, but I don't see the
> problem. Can you help me out here? Does a patch that fixes a memory leak
> not qualify or is it something else?
You forgot to put "Cc: stable..." in the signed-off-by area.
thanks,
greg k-h
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-14 19:43 ` Greg KH
@ 2020-12-14 19:48 ` Tony Krowiak
0 siblings, 0 replies; 15+ messages in thread
From: Tony Krowiak @ 2020-12-14 19:48 UTC (permalink / raw)
To: Greg KH
Cc: linux-s390, linux-kernel, kvm, stable, sashal, borntraeger,
cohuck, kwankhede, pbonzini, alex.williamson, pasic
On 12/14/20 2:43 PM, Greg KH wrote:
> On Mon, Dec 14, 2020 at 02:39:17PM -0500, Tony Krowiak wrote:
>>
>> On 12/14/20 12:07 PM, Greg KH wrote:
>>> On Mon, Dec 14, 2020 at 11:56:17AM -0500, Tony Krowiak wrote:
>>>> The vfio_ap device driver registers a group notifier with VFIO when the
>>>> file descriptor for a VFIO mediated device for a KVM guest is opened to
>>>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
>>>> event). When the KVM pointer is set, the vfio_ap driver takes the
>>>> following actions:
>>>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
>>>> of the mediated device.
>>>> 2. Calls the kvm_get_kvm() function to increment its reference counter.
>>>> 3. Sets the function pointer to the function that handles interception of
>>>> the instruction that enables/disables interrupt processing.
>>>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
>>>> the guest.
>>>>
>>>> In order to avoid memory leaks, when the notifier is called to receive
>>>> notification that the KVM pointer has been set to NULL, the vfio_ap device
>>>> driver should reverse the actions taken when the KVM pointer was set.
>>>>
>>>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>>>> ---
>>>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
>>>> 1 file changed, 20 insertions(+), 9 deletions(-)
>>> <formletter>
>>>
>>> This is not the correct way to submit patches for inclusion in the
>>> stable kernel tree. Please read:
>>> https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
>>> for how to do this properly.
>>>
>>> </formletter>
>> I read the document on the correct way to submit patches for inclusion in
>> the stable kernel. I apologize for my ignorance, but I don't see the
>> problem. Can you help me out here? Does a patch that fixes a memory leak
>> not qualify or is it something else?
> You forgot to put "Cc: stable..." in the signed-off-by area.
>
> thanks,
Option 1, I must be blind. thanks
>
> greg k-h
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-14 16:56 [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated Tony Krowiak
2020-12-14 17:07 ` Greg KH
@ 2020-12-15 10:57 ` Halil Pasic
2020-12-15 18:10 ` Christian Borntraeger
2020-12-15 17:42 ` Cornelia Huck
2020-12-17 0:39 ` Tony Krowiak
3 siblings, 1 reply; 15+ messages in thread
From: Halil Pasic @ 2020-12-15 10:57 UTC (permalink / raw)
To: Tony Krowiak
Cc: linux-s390, linux-kernel, kvm, stable, gregkh, sashal,
borntraeger, cohuck, kwankhede, pbonzini, alex.williamson, pasic
On Mon, 14 Dec 2020 11:56:17 -0500
Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> The vfio_ap device driver registers a group notifier with VFIO when the
> file descriptor for a VFIO mediated device for a KVM guest is opened to
> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> event). When the KVM pointer is set, the vfio_ap driver takes the
> following actions:
> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
> of the mediated device.
> 2. Calls the kvm_get_kvm() function to increment its reference counter.
> 3. Sets the function pointer to the function that handles interception of
> the instruction that enables/disables interrupt processing.
> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
> the guest.
>
> In order to avoid memory leaks, when the notifier is called to receive
> notification that the KVM pointer has been set to NULL, the vfio_ap device
> driver should reverse the actions taken when the KVM pointer was set.
>
> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
> 1 file changed, 20 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index e0bde8518745..cd22e85588e1 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
> {
> struct ap_matrix_mdev *m;
>
> - mutex_lock(&matrix_dev->lock);
> -
> list_for_each_entry(m, &matrix_dev->mdev_list, node) {
> if ((m != matrix_mdev) && (m->kvm == kvm)) {
> mutex_unlock(&matrix_dev->lock);
> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
> matrix_mdev->kvm = kvm;
> kvm_get_kvm(kvm);
> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
> - mutex_unlock(&matrix_dev->lock);
>
> return 0;
> }
> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
> return NOTIFY_DONE;
> }
>
> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
> +{
> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
This patch LGTM. The only concern I have with it is whether a
different cpu is guaranteed to observe the above assignment as
an atomic operation. I think we didn't finish this discussion
at v1, or did we?
Regards,
Halil
> + vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
> + kvm_put_kvm(matrix_mdev->kvm);
> + matrix_mdev->kvm = NULL;
> +}
> +
> static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
> unsigned long action, void *data)
> {
> - int ret;
> + int ret, notify_rc = NOTIFY_DONE;
> struct ap_matrix_mdev *matrix_mdev;
>
> if (action != VFIO_GROUP_NOTIFY_SET_KVM)
> return NOTIFY_OK;
>
> matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
> + mutex_lock(&matrix_dev->lock);
>
> if (!data) {
> - matrix_mdev->kvm = NULL;
> - return NOTIFY_OK;
> + if (matrix_mdev->kvm)
> + vfio_ap_mdev_unset_kvm(matrix_mdev);
> + notify_rc = NOTIFY_OK;
> + goto notify_done;
> }
>
> ret = vfio_ap_mdev_set_kvm(matrix_mdev, data);
> if (ret)
> - return NOTIFY_DONE;
> + goto notify_done;
>
> /* If there is no CRYCB pointer, then we can't copy the masks */
> if (!matrix_mdev->kvm->arch.crypto.crycbd)
> - return NOTIFY_DONE;
> + goto notify_done;
>
> kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm,
> matrix_mdev->matrix.aqm,
> matrix_mdev->matrix.adm);
>
> - return NOTIFY_OK;
> +notify_done:
> + mutex_unlock(&matrix_dev->lock);
> + return notify_rc;
> }
>
> static void vfio_ap_irq_disable_apqn(int apqn)
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-15 10:57 ` Halil Pasic
@ 2020-12-15 18:10 ` Christian Borntraeger
2020-12-16 1:21 ` Halil Pasic
0 siblings, 1 reply; 15+ messages in thread
From: Christian Borntraeger @ 2020-12-15 18:10 UTC (permalink / raw)
To: Halil Pasic, Tony Krowiak
Cc: linux-s390, linux-kernel, kvm, stable, gregkh, sashal, cohuck,
kwankhede, pbonzini, alex.williamson, pasic
On 15.12.20 11:57, Halil Pasic wrote:
> On Mon, 14 Dec 2020 11:56:17 -0500
> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
>
>> The vfio_ap device driver registers a group notifier with VFIO when the
>> file descriptor for a VFIO mediated device for a KVM guest is opened to
>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
>> event). When the KVM pointer is set, the vfio_ap driver takes the
>> following actions:
>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
>> of the mediated device.
>> 2. Calls the kvm_get_kvm() function to increment its reference counter.
>> 3. Sets the function pointer to the function that handles interception of
>> the instruction that enables/disables interrupt processing.
>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
>> the guest.
>>
>> In order to avoid memory leaks, when the notifier is called to receive
>> notification that the KVM pointer has been set to NULL, the vfio_ap device
>> driver should reverse the actions taken when the KVM pointer was set.
>>
>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>> ---
>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
>> 1 file changed, 20 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
>> index e0bde8518745..cd22e85588e1 100644
>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>> {
>> struct ap_matrix_mdev *m;
>>
>> - mutex_lock(&matrix_dev->lock);
>> -
>> list_for_each_entry(m, &matrix_dev->mdev_list, node) {
>> if ((m != matrix_mdev) && (m->kvm == kvm)) {
>> mutex_unlock(&matrix_dev->lock);
>> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>> matrix_mdev->kvm = kvm;
>> kvm_get_kvm(kvm);
>> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
>> - mutex_unlock(&matrix_dev->lock);
>>
>> return 0;
>> }
>> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
>> return NOTIFY_DONE;
>> }
>>
>> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
>> +{
>> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>
>
> This patch LGTM. The only concern I have with it is whether a
> different cpu is guaranteed to observe the above assignment as
> an atomic operation. I think we didn't finish this discussion
> at v1, or did we?
You mean just this assigment:
>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
should either have the old or the new value, but not halve zero halve old?
Normally this should be ok (and I would consider this a compiler bug if
this is split into 2 32 bit zeroes) But if you really want to be sure then we
can use WRITE_ONCE.
I think we take this via the s390 tree? I can add the WRITE_ONCE when applying?
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-15 18:10 ` Christian Borntraeger
@ 2020-12-16 1:21 ` Halil Pasic
2020-12-16 9:58 ` Christian Borntraeger
0 siblings, 1 reply; 15+ messages in thread
From: Halil Pasic @ 2020-12-16 1:21 UTC (permalink / raw)
To: Christian Borntraeger
Cc: Tony Krowiak, linux-s390, linux-kernel, kvm, stable, gregkh,
sashal, cohuck, kwankhede, pbonzini, alex.williamson, pasic
On Tue, 15 Dec 2020 19:10:20 +0100
Christian Borntraeger <borntraeger@de.ibm.com> wrote:
>
>
> On 15.12.20 11:57, Halil Pasic wrote:
> > On Mon, 14 Dec 2020 11:56:17 -0500
> > Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> >
> >> The vfio_ap device driver registers a group notifier with VFIO when the
> >> file descriptor for a VFIO mediated device for a KVM guest is opened to
> >> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> >> event). When the KVM pointer is set, the vfio_ap driver takes the
> >> following actions:
> >> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
> >> of the mediated device.
> >> 2. Calls the kvm_get_kvm() function to increment its reference counter.
> >> 3. Sets the function pointer to the function that handles interception of
> >> the instruction that enables/disables interrupt processing.
> >> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
> >> the guest.
> >>
> >> In order to avoid memory leaks, when the notifier is called to receive
> >> notification that the KVM pointer has been set to NULL, the vfio_ap device
> >> driver should reverse the actions taken when the KVM pointer was set.
> >>
> >> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> >> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> >> ---
> >> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
> >> 1 file changed, 20 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> >> index e0bde8518745..cd22e85588e1 100644
> >> --- a/drivers/s390/crypto/vfio_ap_ops.c
> >> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> >> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
> >> {
> >> struct ap_matrix_mdev *m;
> >>
> >> - mutex_lock(&matrix_dev->lock);
> >> -
> >> list_for_each_entry(m, &matrix_dev->mdev_list, node) {
> >> if ((m != matrix_mdev) && (m->kvm == kvm)) {
> >> mutex_unlock(&matrix_dev->lock);
> >> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
> >> matrix_mdev->kvm = kvm;
> >> kvm_get_kvm(kvm);
> >> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
> >> - mutex_unlock(&matrix_dev->lock);
> >>
> >> return 0;
> >> }
> >> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
> >> return NOTIFY_DONE;
> >> }
> >>
> >> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
> >> +{
> >> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> >> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> >
> >
> > This patch LGTM. The only concern I have with it is whether a
> > different cpu is guaranteed to observe the above assignment as
> > an atomic operation. I think we didn't finish this discussion
> > at v1, or did we?
>
> You mean just this assigment:
> >> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> should either have the old or the new value, but not halve zero halve old?
>
Yes that is the assignment I was referring to. Old value will work as well because
kvm holds a reference to this module while in the pqap_hook.
> Normally this should be ok (and I would consider this a compiler bug if
> this is split into 2 32 bit zeroes) But if you really want to be sure then we
> can use WRITE_ONCE.
Just my curiosity: what would make this a bug? Is it the s390 elf ABI,
or some gcc feature, or even the C standard? Also how exactly would
WRITE_ONCE, also access via volatile help in this particular situation?
I agree, if the member is properly aligned, (which it is),
normally/probably we are fine on s390x (which is also a given).
> I think we take this via the s390 tree? I can add the WRITE_ONCE when applying?
Yes that works fine with me.
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-16 1:21 ` Halil Pasic
@ 2020-12-16 9:58 ` Christian Borntraeger
2020-12-16 16:05 ` Christian Borntraeger
2020-12-16 22:49 ` Halil Pasic
0 siblings, 2 replies; 15+ messages in thread
From: Christian Borntraeger @ 2020-12-16 9:58 UTC (permalink / raw)
To: Halil Pasic
Cc: Tony Krowiak, linux-s390, linux-kernel, kvm, stable, gregkh,
sashal, cohuck, kwankhede, pbonzini, alex.williamson, pasic
On 16.12.20 02:21, Halil Pasic wrote:
> On Tue, 15 Dec 2020 19:10:20 +0100
> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
>
>>
>>
>> On 15.12.20 11:57, Halil Pasic wrote:
>>> On Mon, 14 Dec 2020 11:56:17 -0500
>>> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
>>>
>>>> The vfio_ap device driver registers a group notifier with VFIO when the
>>>> file descriptor for a VFIO mediated device for a KVM guest is opened to
>>>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
>>>> event). When the KVM pointer is set, the vfio_ap driver takes the
>>>> following actions:
>>>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
>>>> of the mediated device.
>>>> 2. Calls the kvm_get_kvm() function to increment its reference counter.
>>>> 3. Sets the function pointer to the function that handles interception of
>>>> the instruction that enables/disables interrupt processing.
>>>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
>>>> the guest.
>>>>
>>>> In order to avoid memory leaks, when the notifier is called to receive
>>>> notification that the KVM pointer has been set to NULL, the vfio_ap device
>>>> driver should reverse the actions taken when the KVM pointer was set.
>>>>
>>>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>>>> ---
>>>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
>>>> 1 file changed, 20 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
>>>> index e0bde8518745..cd22e85588e1 100644
>>>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>>>> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>>>> {
>>>> struct ap_matrix_mdev *m;
>>>>
>>>> - mutex_lock(&matrix_dev->lock);
>>>> -
>>>> list_for_each_entry(m, &matrix_dev->mdev_list, node) {
>>>> if ((m != matrix_mdev) && (m->kvm == kvm)) {
>>>> mutex_unlock(&matrix_dev->lock);
>>>> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>>>> matrix_mdev->kvm = kvm;
>>>> kvm_get_kvm(kvm);
>>>> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
>>>> - mutex_unlock(&matrix_dev->lock);
>>>>
>>>> return 0;
>>>> }
>>>> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
>>>> return NOTIFY_DONE;
>>>> }
>>>>
>>>> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
>>>> +{
>>>> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
>>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>>>
>>>
>>> This patch LGTM. The only concern I have with it is whether a
>>> different cpu is guaranteed to observe the above assignment as
>>> an atomic operation. I think we didn't finish this discussion
>>> at v1, or did we?
>>
>> You mean just this assigment:
>>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>> should either have the old or the new value, but not halve zero halve old?
>>
>
> Yes that is the assignment I was referring to. Old value will work as well because
> kvm holds a reference to this module while in the pqap_hook.
>
>> Normally this should be ok (and I would consider this a compiler bug if
>> this is split into 2 32 bit zeroes) But if you really want to be sure then we
>> can use WRITE_ONCE.
>
> Just my curiosity: what would make this a bug? Is it the s390 elf ABI,
> or some gcc feature, or even the C standard? Also how exactly would
> WRITE_ONCE, also access via volatile help in this particular situation?
I think its a tricky things and not strictly guaranteed, but there is a lot
of code that relies on the atomicity of word sizes. see for example the discussion
here
https://lore.kernel.org/lkml/CAHk-=wgC4+kV9AiLokw7cPP429rKCU+vjA8cWAfyOjC3MtqC4A@mail.gmail.com/
WRITE_ONCE will not change the guarantees a lot, but it is mostly a documentation
that we assume atomic access here.
>
> I agree, if the member is properly aligned, (which it is),
> normally/probably we are fine on s390x (which is also a given).
>
>> I think we take this via the s390 tree? I can add the WRITE_ONCE when applying?
>
> Yes that works fine with me.
>
> Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
>
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-16 9:58 ` Christian Borntraeger
@ 2020-12-16 16:05 ` Christian Borntraeger
2020-12-16 22:00 ` Halil Pasic
2020-12-17 0:46 ` Tony Krowiak
2020-12-16 22:49 ` Halil Pasic
1 sibling, 2 replies; 15+ messages in thread
From: Christian Borntraeger @ 2020-12-16 16:05 UTC (permalink / raw)
To: Halil Pasic
Cc: Tony Krowiak, linux-s390, linux-kernel, kvm, cohuck, kwankhede,
pbonzini, alex.williamson, pasic
On 16.12.20 10:58, Christian Borntraeger wrote:
> On 16.12.20 02:21, Halil Pasic wrote:
>> On Tue, 15 Dec 2020 19:10:20 +0100
>> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
>>
>>>
>>>
>>> On 15.12.20 11:57, Halil Pasic wrote:
>>>> On Mon, 14 Dec 2020 11:56:17 -0500
>>>> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
>>>>
>>>>> The vfio_ap device driver registers a group notifier with VFIO when the
>>>>> file descriptor for a VFIO mediated device for a KVM guest is opened to
>>>>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
>>>>> event). When the KVM pointer is set, the vfio_ap driver takes the
>>>>> following actions:
>>>>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
>>>>> of the mediated device.
>>>>> 2. Calls the kvm_get_kvm() function to increment its reference counter.
>>>>> 3. Sets the function pointer to the function that handles interception of
>>>>> the instruction that enables/disables interrupt processing.
>>>>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
>>>>> the guest.
>>>>>
>>>>> In order to avoid memory leaks, when the notifier is called to receive
>>>>> notification that the KVM pointer has been set to NULL, the vfio_ap device
>>>>> driver should reverse the actions taken when the KVM pointer was set.
>>>>>
>>>>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
>>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>>>>> ---
>>>>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
>>>>> 1 file changed, 20 insertions(+), 9 deletions(-)
>>>>>
>>>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
>>>>> index e0bde8518745..cd22e85588e1 100644
>>>>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>>>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>>>>> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>>>>> {
>>>>> struct ap_matrix_mdev *m;
>>>>>
>>>>> - mutex_lock(&matrix_dev->lock);
>>>>> -
>>>>> list_for_each_entry(m, &matrix_dev->mdev_list, node) {
>>>>> if ((m != matrix_mdev) && (m->kvm == kvm)) {
>>>>> mutex_unlock(&matrix_dev->lock);
>>>>> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>>>>> matrix_mdev->kvm = kvm;
>>>>> kvm_get_kvm(kvm);
>>>>> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
>>>>> - mutex_unlock(&matrix_dev->lock);
>>>>>
>>>>> return 0;
>>>>> }
>>>>> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
>>>>> return NOTIFY_DONE;
>>>>> }
>>>>>
>>>>> +static void "(struct ap_matrix_mdev *matrix_mdev)
>>>>> +{
>>>>> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
>>>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>>>>
>>>>
>>>> This patch LGTM. The only concern I have with it is whether a
>>>> different cpu is guaranteed to observe the above assignment as
>>>> an atomic operation. I think we didn't finish this discussion
>>>> at v1, or did we?
>>>
>>> You mean just this assigment:
>>>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>>> should either have the old or the new value, but not halve zero halve old?
>>>
>>
>> Yes that is the assignment I was referring to. Old value will work as well because
>> kvm holds a reference to this module while in the pqap_hook.
>>
>>> Normally this should be ok (and I would consider this a compiler bug if
>>> this is split into 2 32 bit zeroes) But if you really want to be sure then we
>>> can use WRITE_ONCE.
>>
>> Just my curiosity: what would make this a bug? Is it the s390 elf ABI,
>> or some gcc feature, or even the C standard? Also how exactly would
>> WRITE_ONCE, also access via volatile help in this particular situation?
>
> I think its a tricky things and not strictly guaranteed, but there is a lot
> of code that relies on the atomicity of word sizes. see for example the discussion
> here
> https://lore.kernel.org/lkml/CAHk-=wgC4+kV9AiLokw7cPP429rKCU+vjA8cWAfyOjC3MtqC4A@mail.gmail.com/
>
> WRITE_ONCE will not change the guarantees a lot, but it is mostly a documentation
> that we assume atomic access here.
After looking again at the code, I think I have to correct myself.
WRITE_ONCE does not look necessary.
Another thing, though:
Shouldnt we also replace this code
[...]
static void vfio_ap_mdev_release(struct mdev_device *mdev)
{
struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
mutex_lock(&matrix_dev->lock);
if (matrix_mdev->kvm) {
---> kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
---> matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
---> vfio_ap_mdev_reset_queues(mdev);
---> kvm_put_kvm(matrix_mdev->kvm);
---> matrix_mdev->kvm = NULL;
[...]
with vfio_ap_mdev_unset_kvm ?
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-16 16:05 ` Christian Borntraeger
@ 2020-12-16 22:00 ` Halil Pasic
2020-12-17 0:46 ` Tony Krowiak
1 sibling, 0 replies; 15+ messages in thread
From: Halil Pasic @ 2020-12-16 22:00 UTC (permalink / raw)
To: Christian Borntraeger
Cc: Tony Krowiak, linux-s390, linux-kernel, kvm, cohuck, kwankhede,
pbonzini, alex.williamson, pasic
On Wed, 16 Dec 2020 17:05:24 +0100
Christian Borntraeger <borntraeger@de.ibm.com> wrote:
>
>
> On 16.12.20 10:58, Christian Borntraeger wrote:
> > On 16.12.20 02:21, Halil Pasic wrote:
> >> On Tue, 15 Dec 2020 19:10:20 +0100
> >> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> >>
> >>>
> >>>
> >>> On 15.12.20 11:57, Halil Pasic wrote:
> >>>> On Mon, 14 Dec 2020 11:56:17 -0500
> >>>> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> >>>>
> >>>>> The vfio_ap device driver registers a group notifier with VFIO when the
> >>>>> file descriptor for a VFIO mediated device for a KVM guest is opened to
> >>>>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> >>>>> event). When the KVM pointer is set, the vfio_ap driver takes the
> >>>>> following actions:
> >>>>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
> >>>>> of the mediated device.
> >>>>> 2. Calls the kvm_get_kvm() function to increment its reference counter.
> >>>>> 3. Sets the function pointer to the function that handles interception of
> >>>>> the instruction that enables/disables interrupt processing.
> >>>>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
> >>>>> the guest.
> >>>>>
> >>>>> In order to avoid memory leaks, when the notifier is called to receive
> >>>>> notification that the KVM pointer has been set to NULL, the vfio_ap device
> >>>>> driver should reverse the actions taken when the KVM pointer was set.
> >>>>>
> >>>>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> >>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> >>>>> ---
> >>>>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
> >>>>> 1 file changed, 20 insertions(+), 9 deletions(-)
> >>>>>
> >>>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> >>>>> index e0bde8518745..cd22e85588e1 100644
> >>>>> --- a/drivers/s390/crypto/vfio_ap_ops.c
> >>>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> >>>>> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
> >>>>> {
> >>>>> struct ap_matrix_mdev *m;
> >>>>>
> >>>>> - mutex_lock(&matrix_dev->lock);
> >>>>> -
> >>>>> list_for_each_entry(m, &matrix_dev->mdev_list, node) {
> >>>>> if ((m != matrix_mdev) && (m->kvm == kvm)) {
> >>>>> mutex_unlock(&matrix_dev->lock);
> >>>>> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
> >>>>> matrix_mdev->kvm = kvm;
> >>>>> kvm_get_kvm(kvm);
> >>>>> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
> >>>>> - mutex_unlock(&matrix_dev->lock);
> >>>>>
> >>>>> return 0;
> >>>>> }
> >>>>> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
> >>>>> return NOTIFY_DONE;
> >>>>> }
> >>>>>
> >>>>> +static void "(struct ap_matrix_mdev *matrix_mdev)
> >>>>> +{
> >>>>> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> >>>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> >>>>
> >>>>
> >>>> This patch LGTM. The only concern I have with it is whether a
> >>>> different cpu is guaranteed to observe the above assignment as
> >>>> an atomic operation. I think we didn't finish this discussion
> >>>> at v1, or did we?
> >>>
> >>> You mean just this assigment:
> >>>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> >>> should either have the old or the new value, but not halve zero halve old?
> >>>
> >>
> >> Yes that is the assignment I was referring to. Old value will work as well because
> >> kvm holds a reference to this module while in the pqap_hook.
> >>
> >>> Normally this should be ok (and I would consider this a compiler bug if
> >>> this is split into 2 32 bit zeroes) But if you really want to be sure then we
> >>> can use WRITE_ONCE.
> >>
> >> Just my curiosity: what would make this a bug? Is it the s390 elf ABI,
> >> or some gcc feature, or even the C standard? Also how exactly would
> >> WRITE_ONCE, also access via volatile help in this particular situation?
> >
> > I think its a tricky things and not strictly guaranteed, but there is a lot
> > of code that relies on the atomicity of word sizes. see for example the discussion
> > here
> > https://lore.kernel.org/lkml/CAHk-=wgC4+kV9AiLokw7cPP429rKCU+vjA8cWAfyOjC3MtqC4A@mail.gmail.com/
> >
> > WRITE_ONCE will not change the guarantees a lot, but it is mostly a documentation
> > that we assume atomic access here.
>
> After looking again at the code, I think I have to correct myself.
> WRITE_ONCE does not look necessary.
>
Yes, volatile access is not about atomic access. Whether a volatile
access here is a good idea or not, is a different question.
>
> Another thing, though:
> Shouldnt we also replace this code
>
> [...]
> static void vfio_ap_mdev_release(struct mdev_device *mdev)
> {
> struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>
> mutex_lock(&matrix_dev->lock);
> if (matrix_mdev->kvm) {
> ---> kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> ---> matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> ---> vfio_ap_mdev_reset_queues(mdev);
> ---> kvm_put_kvm(matrix_mdev->kvm);
> ---> matrix_mdev->kvm = NULL;
> [...]
>
> with vfio_ap_mdev_unset_kvm ?
Yes, we had something like this in v2 already. Would be good style to
do so.
Regards,
Halil
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-16 16:05 ` Christian Borntraeger
2020-12-16 22:00 ` Halil Pasic
@ 2020-12-17 0:46 ` Tony Krowiak
1 sibling, 0 replies; 15+ messages in thread
From: Tony Krowiak @ 2020-12-17 0:46 UTC (permalink / raw)
To: Christian Borntraeger, Halil Pasic
Cc: linux-s390, linux-kernel, kvm, cohuck, kwankhede, pbonzini,
alex.williamson, pasic
On 12/16/20 11:05 AM, Christian Borntraeger wrote:
>
> On 16.12.20 10:58, Christian Borntraeger wrote:
>> On 16.12.20 02:21, Halil Pasic wrote:
>>> On Tue, 15 Dec 2020 19:10:20 +0100
>>> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
>>>
>>>>
>>>> On 15.12.20 11:57, Halil Pasic wrote:
>>>>> On Mon, 14 Dec 2020 11:56:17 -0500
>>>>> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
>>>>>
>>>>>> The vfio_ap device driver registers a group notifier with VFIO when the
>>>>>> file descriptor for a VFIO mediated device for a KVM guest is opened to
>>>>>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
>>>>>> event). When the KVM pointer is set, the vfio_ap driver takes the
>>>>>> following actions:
>>>>>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
>>>>>> of the mediated device.
>>>>>> 2. Calls the kvm_get_kvm() function to increment its reference counter.
>>>>>> 3. Sets the function pointer to the function that handles interception of
>>>>>> the instruction that enables/disables interrupt processing.
>>>>>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
>>>>>> the guest.
>>>>>>
>>>>>> In order to avoid memory leaks, when the notifier is called to receive
>>>>>> notification that the KVM pointer has been set to NULL, the vfio_ap device
>>>>>> driver should reverse the actions taken when the KVM pointer was set.
>>>>>>
>>>>>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
>>>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>>>>>> ---
>>>>>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
>>>>>> 1 file changed, 20 insertions(+), 9 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
>>>>>> index e0bde8518745..cd22e85588e1 100644
>>>>>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>>>>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>>>>>> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>>>>>> {
>>>>>> struct ap_matrix_mdev *m;
>>>>>>
>>>>>> - mutex_lock(&matrix_dev->lock);
>>>>>> -
>>>>>> list_for_each_entry(m, &matrix_dev->mdev_list, node) {
>>>>>> if ((m != matrix_mdev) && (m->kvm == kvm)) {
>>>>>> mutex_unlock(&matrix_dev->lock);
>>>>>> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>>>>>> matrix_mdev->kvm = kvm;
>>>>>> kvm_get_kvm(kvm);
>>>>>> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
>>>>>> - mutex_unlock(&matrix_dev->lock);
>>>>>>
>>>>>> return 0;
>>>>>> }
>>>>>> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
>>>>>> return NOTIFY_DONE;
>>>>>> }
>>>>>>
>>>>>> +static void "(struct ap_matrix_mdev *matrix_mdev)
>>>>>> +{
>>>>>> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
>>>>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>>>>>
>>>>> This patch LGTM. The only concern I have with it is whether a
>>>>> different cpu is guaranteed to observe the above assignment as
>>>>> an atomic operation. I think we didn't finish this discussion
>>>>> at v1, or did we?
>>>> You mean just this assigment:
>>>>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>>>> should either have the old or the new value, but not halve zero halve old?
>>>>
>>> Yes that is the assignment I was referring to. Old value will work as well because
>>> kvm holds a reference to this module while in the pqap_hook.
>>>
>>>> Normally this should be ok (and I would consider this a compiler bug if
>>>> this is split into 2 32 bit zeroes) But if you really want to be sure then we
>>>> can use WRITE_ONCE.
>>> Just my curiosity: what would make this a bug? Is it the s390 elf ABI,
>>> or some gcc feature, or even the C standard? Also how exactly would
>>> WRITE_ONCE, also access via volatile help in this particular situation?
>> I think its a tricky things and not strictly guaranteed, but there is a lot
>> of code that relies on the atomicity of word sizes. see for example the discussion
>> here
>> https://lore.kernel.org/lkml/CAHk-=wgC4+kV9AiLokw7cPP429rKCU+vjA8cWAfyOjC3MtqC4A@mail.gmail.com/
>>
>> WRITE_ONCE will not change the guarantees a lot, but it is mostly a documentation
>> that we assume atomic access here.
> After looking again at the code, I think I have to correct myself.
> WRITE_ONCE does not look necessary.
>
>
> Another thing, though:
> Shouldnt we also replace this code
>
> [...]
> static void vfio_ap_mdev_release(struct mdev_device *mdev)
> {
> struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>
> mutex_lock(&matrix_dev->lock);
> if (matrix_mdev->kvm) {
> ---> kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> ---> matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> ---> vfio_ap_mdev_reset_queues(mdev);
> ---> kvm_put_kvm(matrix_mdev->kvm);
> ---> matrix_mdev->kvm = NULL;
> [...]
>
> with vfio_ap_mdev_unset_kvm ?
I had that in the v2 patches, but mistakenly removed it
because of a misinterpretation of the docs on posting a
patch for a stable release. I'll restore it since I have to
remove the unlock from the vfio_ap_mdev_unset_kvm
function.
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-16 9:58 ` Christian Borntraeger
2020-12-16 16:05 ` Christian Borntraeger
@ 2020-12-16 22:49 ` Halil Pasic
1 sibling, 0 replies; 15+ messages in thread
From: Halil Pasic @ 2020-12-16 22:49 UTC (permalink / raw)
To: Christian Borntraeger
Cc: Tony Krowiak, linux-s390, linux-kernel, kvm, stable, gregkh,
sashal, cohuck, kwankhede, pbonzini, alex.williamson, pasic
On Wed, 16 Dec 2020 10:58:48 +0100
Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> On 16.12.20 02:21, Halil Pasic wrote:
> > On Tue, 15 Dec 2020 19:10:20 +0100
> > Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> >
> >>
> >>
> >> On 15.12.20 11:57, Halil Pasic wrote:
> >>> On Mon, 14 Dec 2020 11:56:17 -0500
> >>> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> >>>
> >>>> The vfio_ap device driver registers a group notifier with VFIO when the
> >>>> file descriptor for a VFIO mediated device for a KVM guest is opened to
> >>>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> >>>> event). When the KVM pointer is set, the vfio_ap driver takes the
> >>>> following actions:
> >>>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
> >>>> of the mediated device.
> >>>> 2. Calls the kvm_get_kvm() function to increment its reference counter.
> >>>> 3. Sets the function pointer to the function that handles interception of
> >>>> the instruction that enables/disables interrupt processing.
> >>>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
> >>>> the guest.
> >>>>
> >>>> In order to avoid memory leaks, when the notifier is called to receive
> >>>> notification that the KVM pointer has been set to NULL, the vfio_ap device
> >>>> driver should reverse the actions taken when the KVM pointer was set.
> >>>>
> >>>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> >>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> >>>> ---
> >>>> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
> >>>> 1 file changed, 20 insertions(+), 9 deletions(-)
> >>>>
> >>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> >>>> index e0bde8518745..cd22e85588e1 100644
> >>>> --- a/drivers/s390/crypto/vfio_ap_ops.c
> >>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> >>>> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
> >>>> {
> >>>> struct ap_matrix_mdev *m;
> >>>>
> >>>> - mutex_lock(&matrix_dev->lock);
> >>>> -
> >>>> list_for_each_entry(m, &matrix_dev->mdev_list, node) {
> >>>> if ((m != matrix_mdev) && (m->kvm == kvm)) {
> >>>> mutex_unlock(&matrix_dev->lock);
> >>>> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
> >>>> matrix_mdev->kvm = kvm;
> >>>> kvm_get_kvm(kvm);
> >>>> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
> >>>> - mutex_unlock(&matrix_dev->lock);
> >>>>
> >>>> return 0;
> >>>> }
> >>>> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
> >>>> return NOTIFY_DONE;
> >>>> }
> >>>>
> >>>> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
> >>>> +{
> >>>> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> >>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> >>>
> >>>
> >>> This patch LGTM. The only concern I have with it is whether a
> >>> different cpu is guaranteed to observe the above assignment as
> >>> an atomic operation. I think we didn't finish this discussion
> >>> at v1, or did we?
> >>
> >> You mean just this assigment:
> >>>> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> >> should either have the old or the new value, but not halve zero halve old?
> >>
> >
> > Yes that is the assignment I was referring to. Old value will work as well because
> > kvm holds a reference to this module while in the pqap_hook.
> >
> >> Normally this should be ok (and I would consider this a compiler bug if
> >> this is split into 2 32 bit zeroes) But if you really want to be sure then we
> >> can use WRITE_ONCE.
> >
> > Just my curiosity: what would make this a bug? Is it the s390 elf ABI,
> > or some gcc feature, or even the C standard? Also how exactly would
> > WRITE_ONCE, also access via volatile help in this particular situation?
>
> I think its a tricky things and not strictly guaranteed, but there is a lot
> of code that relies on the atomicity of word sizes. see for example the discussion
> here
> https://lore.kernel.org/lkml/CAHk-=wgC4+kV9AiLokw7cPP429rKCU+vjA8cWAfyOjC3MtqC4A@mail.gmail.com/
>
> WRITE_ONCE will not change the guarantees a lot, but it is mostly a documentation
> that we assume atomic access here.
Thanks a lot! I've read it, and IMHO it seems to contradict the section
https://lwn.net/Articles/793253/#Store%20Tearing a little. From there, I also learned
that WRITE_ONCE (i.e. volatile access) can help, although I don't really
understand why. Of course, we don't need to be portable here, as this
is s390 only code. So we might be safe without anything -- I don't know.
I believe, if volatile were enough (under any circumstances), the C
standard wouldn't have introduced atomic types.
Regards,
Halil
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-14 16:56 [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated Tony Krowiak
2020-12-14 17:07 ` Greg KH
2020-12-15 10:57 ` Halil Pasic
@ 2020-12-15 17:42 ` Cornelia Huck
2020-12-17 0:39 ` Tony Krowiak
3 siblings, 0 replies; 15+ messages in thread
From: Cornelia Huck @ 2020-12-15 17:42 UTC (permalink / raw)
To: Tony Krowiak
Cc: linux-s390, linux-kernel, kvm, stable, gregkh, sashal,
borntraeger, kwankhede, pbonzini, alex.williamson, pasic
On Mon, 14 Dec 2020 11:56:17 -0500
Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> The vfio_ap device driver registers a group notifier with VFIO when the
> file descriptor for a VFIO mediated device for a KVM guest is opened to
> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> event). When the KVM pointer is set, the vfio_ap driver takes the
> following actions:
> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
> of the mediated device.
> 2. Calls the kvm_get_kvm() function to increment its reference counter.
> 3. Sets the function pointer to the function that handles interception of
> the instruction that enables/disables interrupt processing.
> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
> the guest.
>
> In order to avoid memory leaks, when the notifier is called to receive
> notification that the KVM pointer has been set to NULL, the vfio_ap device
> driver should reverse the actions taken when the KVM pointer was set.
>
> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
> 1 file changed, 20 insertions(+), 9 deletions(-)
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
2020-12-14 16:56 [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated Tony Krowiak
` (2 preceding siblings ...)
2020-12-15 17:42 ` Cornelia Huck
@ 2020-12-17 0:39 ` Tony Krowiak
3 siblings, 0 replies; 15+ messages in thread
From: Tony Krowiak @ 2020-12-17 0:39 UTC (permalink / raw)
To: linux-s390, linux-kernel, kvm
Cc: stable, gregkh, sashal, borntraeger, cohuck, kwankhede, pbonzini,
alex.williamson, pasic
On 12/14/20 11:56 AM, Tony Krowiak wrote:
> The vfio_ap device driver registers a group notifier with VFIO when the
> file descriptor for a VFIO mediated device for a KVM guest is opened to
> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> event). When the KVM pointer is set, the vfio_ap driver takes the
> following actions:
> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
> of the mediated device.
> 2. Calls the kvm_get_kvm() function to increment its reference counter.
> 3. Sets the function pointer to the function that handles interception of
> the instruction that enables/disables interrupt processing.
> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
> the guest.
>
> In order to avoid memory leaks, when the notifier is called to receive
> notification that the KVM pointer has been set to NULL, the vfio_ap device
> driver should reverse the actions taken when the KVM pointer was set.
>
> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
> 1 file changed, 20 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index e0bde8518745..cd22e85588e1 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
> {
> struct ap_matrix_mdev *m;
>
> - mutex_lock(&matrix_dev->lock);
> -
> list_for_each_entry(m, &matrix_dev->mdev_list, node) {
> if ((m != matrix_mdev) && (m->kvm == kvm)) {
> mutex_unlock(&matrix_dev->lock);
This unlock needs to be removed.
> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
> matrix_mdev->kvm = kvm;
> kvm_get_kvm(kvm);
> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
> - mutex_unlock(&matrix_dev->lock);
>
> return 0;
> }
> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
> return NOTIFY_DONE;
> }
>
> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
> +{
> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> + vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
> + kvm_put_kvm(matrix_mdev->kvm);
> + matrix_mdev->kvm = NULL;
> +}
> +
> static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
> unsigned long action, void *data)
> {
> - int ret;
> + int ret, notify_rc = NOTIFY_DONE;
> struct ap_matrix_mdev *matrix_mdev;
>
> if (action != VFIO_GROUP_NOTIFY_SET_KVM)
> return NOTIFY_OK;
>
> matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
> + mutex_lock(&matrix_dev->lock);
>
> if (!data) {
> - matrix_mdev->kvm = NULL;
> - return NOTIFY_OK;
> + if (matrix_mdev->kvm)
> + vfio_ap_mdev_unset_kvm(matrix_mdev);
> + notify_rc = NOTIFY_OK;
> + goto notify_done;
> }
>
> ret = vfio_ap_mdev_set_kvm(matrix_mdev, data);
> if (ret)
> - return NOTIFY_DONE;
> + goto notify_done;
>
> /* If there is no CRYCB pointer, then we can't copy the masks */
> if (!matrix_mdev->kvm->arch.crypto.crycbd)
> - return NOTIFY_DONE;
> + goto notify_done;
>
> kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm,
> matrix_mdev->matrix.aqm,
> matrix_mdev->matrix.adm);
>
> - return NOTIFY_OK;
> +notify_done:
> + mutex_unlock(&matrix_dev->lock);
> + return notify_rc;
> }
>
> static void vfio_ap_irq_disable_apqn(int apqn)
^ permalink raw reply [flat|nested] 15+ messages in thread