linux-kernel - Re: [PATCH v2 12/30] s390/pci: get SHM information from list pci

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Message-ID: <20220126111300.1084623e@p-imbrenda>
Date:   Wed, 26 Jan 2022 11:13:00 +0100
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     Pierre Morel <pmorel@...ux.ibm.com>
Cc:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        linux-s390@...r.kernel.org, alex.williamson@...hat.com,
        cohuck@...hat.com, schnelle@...ux.ibm.com, farman@...ux.ibm.com,
        borntraeger@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        frankja@...ux.ibm.com, david@...hat.com, vneethv@...ux.ibm.com,
        oberpar@...ux.ibm.com, freude@...ux.ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 12/30] s390/pci: get SHM information from list pci

On Tue, 18 Jan 2022 11:36:06 +0100
Pierre Morel <pmorel@...ux.ibm.com> wrote:

> On 1/14/22 21:31, Matthew Rosato wrote:
> > KVM will need information on the special handle mask used to indicate
> > emulated devices.  In order to obtain this, a new type of list pci call
> > must be made to gather the information.  Extend clp_list_pci_req to
> > also fetch the model-dependent-data field that holds this mask.
> > 
> > Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
> > ---
> >   arch/s390/include/asm/pci.h     |  1 +
> >   arch/s390/include/asm/pci_clp.h |  2 +-
> >   arch/s390/pci/pci_clp.c         | 28 +++++++++++++++++++++++++---
> >   3 files changed, 27 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
> > index 00a2c24d6d2b..f3cd2da8128c 100644
> > --- a/arch/s390/include/asm/pci.h
> > +++ b/arch/s390/include/asm/pci.h
> > @@ -227,6 +227,7 @@ int clp_enable_fh(struct zpci_dev *zdev, u32 *fh, u8 nr_dma_as);
> >   int clp_disable_fh(struct zpci_dev *zdev, u32 *fh);
> >   int clp_get_state(u32 fid, enum zpci_state *state);
> >   int clp_refresh_fh(u32 fid, u32 *fh);
> > +int zpci_get_mdd(u32 *mdd);
> >   
> >   /* UID */
> >   void update_uid_checking(bool new);
> > diff --git a/arch/s390/include/asm/pci_clp.h b/arch/s390/include/asm/pci_clp.h
> > index 124fadfb74b9..d6bc324763f3 100644
> > --- a/arch/s390/include/asm/pci_clp.h
> > +++ b/arch/s390/include/asm/pci_clp.h
> > @@ -76,7 +76,7 @@ struct clp_req_list_pci {
> >   struct clp_rsp_list_pci {
> >   	struct clp_rsp_hdr hdr;
> >   	u64 resume_token;
> > -	u32 reserved2;
> > +	u32 mdd;
> >   	u16 max_fn;
> >   	u8			: 7;
> >   	u8 uid_checking		: 1;
> > diff --git a/arch/s390/pci/pci_clp.c b/arch/s390/pci/pci_clp.c
> > index bc7446566cbc..308ffb93413f 100644
> > --- a/arch/s390/pci/pci_clp.c
> > +++ b/arch/s390/pci/pci_clp.c
> > @@ -328,7 +328,7 @@ int clp_disable_fh(struct zpci_dev *zdev, u32 *fh)
> >   }
> >   
> >   static int clp_list_pci_req(struct clp_req_rsp_list_pci *rrb,
> > -			    u64 *resume_token, int *nentries)
> > +			    u64 *resume_token, int *nentries, u32 *mdd)
> >   {
> >   	int rc;
> >   
> > @@ -354,6 +354,8 @@ static int clp_list_pci_req(struct clp_req_rsp_list_pci *rrb,
> >   	*nentries = (rrb->response.hdr.len - LIST_PCI_HDR_LEN) /
> >   		rrb->response.entry_size;
> >   	*resume_token = rrb->response.resume_token;
> > +	if (mdd)
> > +		*mdd = rrb->response.mdd;
> >   
> >   	return rc;
> >   }
> > @@ -365,7 +367,7 @@ static int clp_list_pci(struct clp_req_rsp_list_pci *rrb, void *data,
> >   	int nentries, i, rc;
> >   
> >   	do {
> > -		rc = clp_list_pci_req(rrb, &resume_token, &nentries);
> > +		rc = clp_list_pci_req(rrb, &resume_token, &nentries, NULL);
> >   		if (rc)
> >   			return rc;
> >   		for (i = 0; i < nentries; i++)
> > @@ -383,7 +385,7 @@ static int clp_find_pci(struct clp_req_rsp_list_pci *rrb, u32 fid,
> >   	int nentries, i, rc;
> >   
> >   	do {
> > -		rc = clp_list_pci_req(rrb, &resume_token, &nentries);
> > +		rc = clp_list_pci_req(rrb, &resume_token, &nentries, NULL);
> >   		if (rc)
> >   			return rc;
> >   		fh_list = rrb->response.fh_list;
> > @@ -468,6 +470,26 @@ int clp_get_state(u32 fid, enum zpci_state *state)
> >   	return rc;
> >   }
> >   
> > +int zpci_get_mdd(u32 *mdd)
> > +{
> > +	struct clp_req_rsp_list_pci *rrb;
> > +	u64 resume_token = 0;
> > +	int nentries, rc;
> > +
> > +	if (!mdd)
> > +		return -EINVAL;  
> 
> I think this tests is not useful.
> The caller must take care not to call with a NULL pointer,
> what the only caller today make sure.

what if the caller does it anyway?

I think the test is useful. if passing NULL is a bug, then maybe
consider using BUG_ON, or WARN_ONCE

> 
> 
> > +
> > +	rrb = clp_alloc_block(GFP_KERNEL);
> > +	if (!rrb)
> > +		return -ENOMEM;
> > +
> > +	rc = clp_list_pci_req(rrb, &resume_token, &nentries, mdd);
> > +
> > +	clp_free_block(rrb);
> > +	return rc;
> > +}
> > +EXPORT_SYMBOL_GPL(zpci_get_mdd);
> > +
> >   static int clp_base_slpc(struct clp_req *req, struct clp_req_rsp_slpc *lpcb)
> >   {
> >   	unsigned long limit = PAGE_SIZE - sizeof(lpcb->request);
> >   
>