RE: [PATCH v4 1/5] hisi_acc_vfio_pci: fix XQE dma address error

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Sent: Wednesday, February 26, 2025 12:10 AM
> To: liulongfang <liulongfang@xxxxxxxxxx>
> Cc: jgg@xxxxxxxxxx; Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@xxxxxxxxxx>; Jonathan Cameron
> <jonathan.cameron@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; linuxarm@xxxxxxxxxxxxx
> Subject: Re: [PATCH v4 1/5] hisi_acc_vfio_pci: fix XQE dma address error
> 
> On Tue, 25 Feb 2025 14:27:53 +0800
> Longfang Liu <liulongfang@xxxxxxxxxx> wrote:
> 
> > The dma addresses of EQE and AEQE are wrong after migration and
> > results in guest kernel-mode encryption services  failure.
> > Comparing the definition of hardware registers, we found that
> > there was an error when the data read from the register was
> > combined into an address. Therefore, the address combination
> > sequence needs to be corrected.
> >
> > Even after fixing the above problem, we still have an issue
> > where the Guest from an old kernel can get migrated to
> > new kernel and may result in wrong data.
> >
> > In order to ensure that the address is correct after migration,
> > if an old magic number is detected, the dma address needs to be
> > updated.
> >
> > Fixes: b0eed085903e ("hisi_acc_vfio_pci: Add support for VFIO live
> migration")
> > Signed-off-by: Longfang Liu <liulongfang@xxxxxxxxxx>
> > ---
> >  .../vfio/pci/hisilicon/hisi_acc_vfio_pci.c    | 40 ++++++++++++++++---
> >  .../vfio/pci/hisilicon/hisi_acc_vfio_pci.h    | 14 ++++++-
> >  2 files changed, 46 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
> b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
> > index 451c639299eb..35316984089b 100644
> > --- a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
> > +++ b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
> > @@ -350,6 +350,31 @@ static int vf_qm_func_stop(struct hisi_qm *qm)
> >  	return hisi_qm_mb(qm, QM_MB_CMD_PAUSE_QM, 0, 0, 0);
> >  }
> >
> > +static int vf_qm_version_check(struct acc_vf_data *vf_data, struct device
> *dev)
> > +{
> > +	switch (vf_data->acc_magic) {
> > +	case ACC_DEV_MAGIC_V2:
> > +		if (vf_data->major_ver < ACC_DRV_MAJOR_VER ||
> > +		    vf_data->minor_ver < ACC_DRV_MINOR_VER)
> > +			dev_info(dev, "migration driver version not
> match!\n");
> > +			return -EINVAL;
> > +		break;
> 
> What's your major/minor update strategy?
> 
> Note that minor_ver is a u16 and ACC_DRV_MINOR_VER is defined as 0, so
> testing less than 0 against an unsigned is useless.
> 
> Arguably testing major and minor independently is pretty useless too.
> 
> You're defining what a future "old" driver version will accept, which
> is very nearly anything, so any breaking change *again* requires a new
> magic, so we're accomplishing very little here.
> 
> Maybe you want to consider a strategy where you'd increment the major
> number for a breaking change and minor for a compatible feature.  In
> that case you'd want to verify the major_ver matches
> ACC_DRV_MAJOR_VER
> exactly and minor_ver would be more of a feature level.

Agree. I think the above check should be just major_ver != ACC_DRV_MAJOR_VER
and we can make use of minor version whenever we need a specific handling for
a feature support.

Also I think it would be good to print the version info above in case of mismatch.

> 
> > +	case ACC_DEV_MAGIC_V1:
> > +		/* Correct dma address */
> > +		vf_data->eqe_dma = vf_data-
> >qm_eqc_dw[QM_XQC_ADDR_HIGH];
> > +		vf_data->eqe_dma <<= QM_XQC_ADDR_OFFSET;
> > +		vf_data->eqe_dma |= vf_data-
> >qm_eqc_dw[QM_XQC_ADDR_LOW];
> > +		vf_data->aeqe_dma = vf_data-
> >qm_aeqc_dw[QM_XQC_ADDR_HIGH];
> > +		vf_data->aeqe_dma <<= QM_XQC_ADDR_OFFSET;
> > +		vf_data->aeqe_dma |= vf_data-
> >qm_aeqc_dw[QM_XQC_ADDR_LOW];
> > +		break;
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  static int vf_qm_check_match(struct hisi_acc_vf_core_device
> *hisi_acc_vdev,
> >  			     struct hisi_acc_vf_migration_file *migf)
> >  {
> > @@ -363,7 +388,8 @@ static int vf_qm_check_match(struct
> hisi_acc_vf_core_device *hisi_acc_vdev,
> >  	if (migf->total_length < QM_MATCH_SIZE || hisi_acc_vdev-
> >match_done)
> >  		return 0;
> >
> > -	if (vf_data->acc_magic != ACC_DEV_MAGIC) {
> > +	ret = vf_qm_version_check(vf_data, dev);
> > +	if (ret) {
> >  		dev_err(dev, "failed to match ACC_DEV_MAGIC\n");
> >  		return -EINVAL;
> >  	}
> > @@ -418,7 +444,9 @@ static int vf_qm_get_match_data(struct
> hisi_acc_vf_core_device *hisi_acc_vdev,
> >  	int vf_id = hisi_acc_vdev->vf_id;
> >  	int ret;
> >
> > -	vf_data->acc_magic = ACC_DEV_MAGIC;
> > +	vf_data->acc_magic = ACC_DEV_MAGIC_V2;
> > +	vf_data->major_ver = ACC_DRV_MAR;
> > +	vf_data->minor_ver = ACC_DRV_MIN;
> 
> Where are "MAR" and "MIN" defined?  I can't see how this would even
> compile.  Thanks,

Yes. Please  make sure to do a compile test and run basic sanity tested even if you
think the changes are minor. Chances are there that you will miss out things like
this.

Thanks,
Shameer