[v4,2/2] virtio: fix PCI config err handling

Message ID 20180824171420.31246-2-bluca@debian.org
State Superseded, archived
Delegated to: Thomas Monjalon
Headers show
Series
  • [v4,1/2] bus/pci: harmonize and document rte_pci_read_config return value
Related show

Checks

Context Check Description
ci/Intel-compilation success Compilation OK
ci/checkpatch success coding style OK

Commit Message

Luca Boccassi Aug. 24, 2018, 5:14 p.m.
From: Brian Russell <brussell@brocade.com>

In virtio_read_caps and vtpci_msix_detect, rte_pci_read_config returns
the number of bytes read from PCI config or < 0 on error.
If less than the expected number of bytes are read then log the
failure and return rather than carrying on with garbage.

Fixes: 6ba1f63b5ab0 ("virtio: support specification 1.0")

Signed-off-by: Brian Russell <brussell@brocade.com>
Signed-off-by: Luca Boccassi <bluca@debian.org>
---
v2: handle additional rte_pci_read_config incomplete reads
v3: do not handle rte_pci_read_config of virtio cap, added in v2,
    as it's less clear what the right thing to do there is
v4: do a more robust check - first check what the vendor is, and
    skip the cap entirely if it's not what we are looking for.

 drivers/net/virtio/virtio_pci.c | 57 ++++++++++++++++++++++++---------
 1 file changed, 42 insertions(+), 15 deletions(-)

Comments

Tiwei Bie Aug. 27, 2018, 5:29 a.m. | #1
On Fri, Aug 24, 2018 at 06:14:20PM +0100, Luca Boccassi wrote:
> From: Brian Russell <brussell@brocade.com>
> 
> In virtio_read_caps and vtpci_msix_detect, rte_pci_read_config returns
> the number of bytes read from PCI config or < 0 on error.
> If less than the expected number of bytes are read then log the
> failure and return rather than carrying on with garbage.
> 
> Fixes: 6ba1f63b5ab0 ("virtio: support specification 1.0")
> 
> Signed-off-by: Brian Russell <brussell@brocade.com>
> Signed-off-by: Luca Boccassi <bluca@debian.org>
> ---
> v2: handle additional rte_pci_read_config incomplete reads
> v3: do not handle rte_pci_read_config of virtio cap, added in v2,
>     as it's less clear what the right thing to do there is
> v4: do a more robust check - first check what the vendor is, and
>     skip the cap entirely if it's not what we are looking for.
> 
>  drivers/net/virtio/virtio_pci.c | 57 ++++++++++++++++++++++++---------
>  1 file changed, 42 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtio_pci.c b/drivers/net/virtio/virtio_pci.c
> index 6bd22e54a6..cfefa9789b 100644
> --- a/drivers/net/virtio/virtio_pci.c
> +++ b/drivers/net/virtio/virtio_pci.c
> @@ -567,16 +567,30 @@ virtio_read_caps(struct rte_pci_device *dev, struct virtio_hw *hw)
>  	}
>  
>  	ret = rte_pci_read_config(dev, &pos, 1, PCI_CAPABILITY_LIST);
> -	if (ret < 0) {
> -		PMD_INIT_LOG(DEBUG, "failed to read pci capability list");
> +	if (ret != 1) {
> +		PMD_INIT_LOG(DEBUG,
> +			     "failed to read pci capability list, ret %d", ret);
>  		return -1;
>  	}
>  
>  	while (pos) {
> +		ret = rte_pci_read_config(dev, &cap, 2, pos);
> +		if (ret != 2) {
> +			PMD_INIT_LOG(DEBUG,
> +				     "failed to read pci cap at pos: %x ret %d",
> +				     pos, ret);
> +			break;
> +		}
> +		if (cap.cap_vndr != PCI_CAP_ID_MSIX &&
> +				cap.cap_vndr != PCI_CAP_ID_VNDR) {
> +			goto next;
> +		}
> +
>  		ret = rte_pci_read_config(dev, &cap, sizeof(cap), pos);
> -		if (ret < 0) {
> -			PMD_INIT_LOG(ERR,
> -				"failed to read pci cap at pos: %x", pos);
> +		if (ret != sizeof(cap)) {
> +			PMD_INIT_LOG(DEBUG,
> +				     "failed to read pci cap at pos: %x ret %d",
> +				     pos, ret);
>  			break;
>  		}
>  

It seems that I didn't make myself clear in my previous
comments. I mean it's better to handle MSIX cap and virtio
cap respectively in this function. Currently we're always
reading them as virtio caps. As we are strictly requiring
that _read_config() should return the required number of
bytes, it's not perfect to require it to return "virtio
cap size" of bytes while we're trying to read a MSIX cap.
So please change the code to something similar to this:

	while (pos) {
		ret = rte_pci_read_config(dev, &cap, 2, pos);
		if (ret != 2) {
			PMD_INIT_LOG(DEBUG,
				     "failed to read pci cap at pos: %x ret %d",
				     pos, ret);
			break;
		}

		if (cap.cap_vndr == PCI_CAP_ID_MSIX) {
			/* Transitional devices would also have this capability,
			 * that's why we also check if msix is enabled.
			 * 1st byte is cap ID; 2nd byte is the position of next
			 * cap; next two bytes are the flags.
			 */
			uint16_t flags;

			ret = rte_pci_read_config(dev, &flags, sizeof(flags),
					pos + 2);
			if (ret != sizeof(flags)) {
				PMD_INIT_LOG(DEBUG,
					"failed to read pci cap at pos: %x ret %d",
					pos + 2, ret);
				break;
			}

			if (flags & PCI_MSIX_ENABLE)
				hw->use_msix = VIRTIO_MSIX_ENABLED;
			else
				hw->use_msix = VIRTIO_MSIX_DISABLED;
		}

		if (cap.cap_vndr != PCI_CAP_ID_VNDR) {
			PMD_INIT_LOG(DEBUG,
				"[%2x] skipping non VNDR cap id: %02x",
				pos, cap.cap_vndr);
			goto next;
		}

		ret = rte_pci_read_config(dev, &cap, sizeof(cap), pos);
		if (ret != sizeof(cap)) {
			PMD_INIT_LOG(DEBUG,
				     "failed to read pci cap at pos: %x ret %d",
				     pos, ret);
			break;
		}

		PMD_INIT_LOG(DEBUG,
			"[%2x] cfg type: %u, bar: %u, offset: %04x, len: %u",
			pos, cap.cfg_type, cap.bar, cap.offset, cap.length);

		switch (cap.cfg_type) {
		......



> @@ -689,25 +703,38 @@ enum virtio_msix_status
>  vtpci_msix_detect(struct rte_pci_device *dev)
>  {
>  	uint8_t pos;
> -	struct virtio_pci_cap cap;
>  	int ret;
>  
>  	ret = rte_pci_read_config(dev, &pos, 1, PCI_CAPABILITY_LIST);
> -	if (ret < 0) {
> -		PMD_INIT_LOG(DEBUG, "failed to read pci capability list");
> +	if (ret != 1) {
> +		PMD_INIT_LOG(DEBUG,
> +			     "failed to read pci capability list, ret %d", ret);
>  		return VIRTIO_MSIX_NONE;
>  	}
>  
>  	while (pos) {
> -		ret = rte_pci_read_config(dev, &cap, sizeof(cap), pos);
> -		if (ret < 0) {
> -			PMD_INIT_LOG(ERR,
> -				"failed to read pci cap at pos: %x", pos);
> +		uint8_t cap[2];
> +
> +		ret = rte_pci_read_config(dev, cap, sizeof(cap), pos);
> +		if (ret != sizeof(cap)) {
> +			PMD_INIT_LOG(DEBUG,
> +				     "failed to read pci cap at pos: %x ret %d",
> +				     pos, ret);
>  			break;
>  		}
>  
> -		if (cap.cap_vndr == PCI_CAP_ID_MSIX) {
> -			uint16_t flags = ((uint16_t *)&cap)[1];
> +		if (cap[0] == PCI_CAP_ID_MSIX) {
> +			uint16_t flags;
> +
> +			ret = rte_pci_read_config(dev, &flags, sizeof(flags),
> +					pos + sizeof(cap));
> +			if (ret != sizeof(flags)) {
> +				PMD_INIT_LOG(DEBUG,
> +					     "failed to read pci cap at pos:"
> +					     " %x ret %d", pos + sizeof(cap),

There is a build error:

In file included from drivers/net/virtio/virtio_pci.c:15:
drivers/net/virtio/virtio_pci.c: In function ‘vtpci_msix_detect’:
drivers/net/virtio/virtio_logs.h:13:3: error: format ‘%x’ expects argument of type ‘unsigned int’, but argument 5 has type ‘long unsigned int’ [-Werror=format=]
   "%s(): " fmt "\n", __func__, ##args)
   ^~~~~~~~
drivers/net/virtio/virtio_pci.c:732:5: note: in expansion of macro ‘PMD_INIT_LOG’
     PMD_INIT_LOG(DEBUG,
     ^~~~~~~~~~~~
drivers/net/virtio/virtio_pci.c:734:14: note: format string is defined here
           " %x ret %d", pos + sizeof(cap),
             ~^
             %lx


> +					     ret);
> +				break;
> +			}
>  
>  			if (flags & PCI_MSIX_ENABLE)
>  				return VIRTIO_MSIX_ENABLED;
> @@ -715,7 +742,7 @@ vtpci_msix_detect(struct rte_pci_device *dev)
>  				return VIRTIO_MSIX_DISABLED;
>  		}
>  
> -		pos = cap.cap_next;
> +		pos = cap[1];
>  	}
>  
>  	return VIRTIO_MSIX_NONE;
> -- 
> 2.18.0
>
Luca Boccassi Aug. 27, 2018, 4:52 p.m. | #2
On Mon, 2018-08-27 at 13:29 +0800, Tiwei Bie wrote:
> On Fri, Aug 24, 2018 at 06:14:20PM +0100, Luca Boccassi wrote:
> > From: Brian Russell <brussell@brocade.com>
> > 
> > In virtio_read_caps and vtpci_msix_detect, rte_pci_read_config
> > returns
> > the number of bytes read from PCI config or < 0 on error.
> > If less than the expected number of bytes are read then log the
> > failure and return rather than carrying on with garbage.
> > 
> > Fixes: 6ba1f63b5ab0 ("virtio: support specification 1.0")
> > 
> > Signed-off-by: Brian Russell <brussell@brocade.com>
> > Signed-off-by: Luca Boccassi <bluca@debian.org>
> > ---
> > v2: handle additional rte_pci_read_config incomplete reads
> > v3: do not handle rte_pci_read_config of virtio cap, added in v2,
> >     as it's less clear what the right thing to do there is
> > v4: do a more robust check - first check what the vendor is, and
> >     skip the cap entirely if it's not what we are looking for.
> > 
> >  drivers/net/virtio/virtio_pci.c | 57 ++++++++++++++++++++++++-----
> > ----
> >  1 file changed, 42 insertions(+), 15 deletions(-)
> > 
> > diff --git a/drivers/net/virtio/virtio_pci.c
> > b/drivers/net/virtio/virtio_pci.c
> > index 6bd22e54a6..cfefa9789b 100644
> > --- a/drivers/net/virtio/virtio_pci.c
> > +++ b/drivers/net/virtio/virtio_pci.c
> > @@ -567,16 +567,30 @@ virtio_read_caps(struct rte_pci_device *dev,
> > struct virtio_hw *hw)
> >  	}
> >  
> >  	ret = rte_pci_read_config(dev, &pos, 1,
> > PCI_CAPABILITY_LIST);
> > -	if (ret < 0) {
> > -		PMD_INIT_LOG(DEBUG, "failed to read pci capability
> > list");
> > +	if (ret != 1) {
> > +		PMD_INIT_LOG(DEBUG,
> > +			     "failed to read pci capability list,
> > ret %d", ret);
> >  		return -1;
> >  	}
> >  
> >  	while (pos) {
> > +		ret = rte_pci_read_config(dev, &cap, 2, pos);
> > +		if (ret != 2) {
> > +			PMD_INIT_LOG(DEBUG,
> > +				     "failed to read pci cap at
> > pos: %x ret %d",
> > +				     pos, ret);
> > +			break;
> > +		}
> > +		if (cap.cap_vndr != PCI_CAP_ID_MSIX &&
> > +				cap.cap_vndr != PCI_CAP_ID_VNDR) {
> > +			goto next;
> > +		}
> > +
> >  		ret = rte_pci_read_config(dev, &cap, sizeof(cap),
> > pos);
> > -		if (ret < 0) {
> > -			PMD_INIT_LOG(ERR,
> > -				"failed to read pci cap at pos:
> > %x", pos);
> > +		if (ret != sizeof(cap)) {
> > +			PMD_INIT_LOG(DEBUG,
> > +				     "failed to read pci cap at
> > pos: %x ret %d",
> > +				     pos, ret);
> >  			break;
> >  		}
> >  
> 
> It seems that I didn't make myself clear in my previous
> comments. I mean it's better to handle MSIX cap and virtio
> cap respectively in this function. Currently we're always
> reading them as virtio caps. As we are strictly requiring
> that _read_config() should return the required number of
> bytes, it's not perfect to require it to return "virtio
> cap size" of bytes while we're trying to read a MSIX cap.
> So please change the code to something similar to this:

Sorry, though you meant in the vtpci_msix_detect function, which I
changed. Fixed in v5.

> > @@ -689,25 +703,38 @@ enum virtio_msix_status
> >  vtpci_msix_detect(struct rte_pci_device *dev)
> >  {
> >  	uint8_t pos;
> > -	struct virtio_pci_cap cap;
> >  	int ret;
> >  
> >  	ret = rte_pci_read_config(dev, &pos, 1,
> > PCI_CAPABILITY_LIST);
> > -	if (ret < 0) {
> > -		PMD_INIT_LOG(DEBUG, "failed to read pci capability
> > list");
> > +	if (ret != 1) {
> > +		PMD_INIT_LOG(DEBUG,
> > +			     "failed to read pci capability list,
> > ret %d", ret);
> >  		return VIRTIO_MSIX_NONE;
> >  	}
> >  
> >  	while (pos) {
> > -		ret = rte_pci_read_config(dev, &cap, sizeof(cap),
> > pos);
> > -		if (ret < 0) {
> > -			PMD_INIT_LOG(ERR,
> > -				"failed to read pci cap at pos:
> > %x", pos);
> > +		uint8_t cap[2];
> > +
> > +		ret = rte_pci_read_config(dev, cap, sizeof(cap),
> > pos);
> > +		if (ret != sizeof(cap)) {
> > +			PMD_INIT_LOG(DEBUG,
> > +				     "failed to read pci cap at
> > pos: %x ret %d",
> > +				     pos, ret);
> >  			break;
> >  		}
> >  
> > -		if (cap.cap_vndr == PCI_CAP_ID_MSIX) {
> > -			uint16_t flags = ((uint16_t *)&cap)[1];
> > +		if (cap[0] == PCI_CAP_ID_MSIX) {
> > +			uint16_t flags;
> > +
> > +			ret = rte_pci_read_config(dev, &flags,
> > sizeof(flags),
> > +					pos + sizeof(cap));
> > +			if (ret != sizeof(flags)) {
> > +				PMD_INIT_LOG(DEBUG,
> > +					     "failed to read pci
> > cap at pos:"
> > +					     " %x ret %d", pos +
> > sizeof(cap),
> 
> There is a build error:
> 
> In file included from drivers/net/virtio/virtio_pci.c:15:
> drivers/net/virtio/virtio_pci.c: In function ‘vtpci_msix_detect’:
> drivers/net/virtio/virtio_logs.h:13:3: error: format ‘%x’ expects
> argument of type ‘unsigned int’, but argument 5 has type ‘long
> unsigned int’ [-Werror=format=]
>    "%s(): " fmt "\n", __func__, ##args)
>    ^~~~~~~~
> drivers/net/virtio/virtio_pci.c:732:5: note: in expansion of macro
> ‘PMD_INIT_LOG’
>      PMD_INIT_LOG(DEBUG,
>      ^~~~~~~~~~~~
> drivers/net/virtio/virtio_pci.c:734:14: note: format string is
> defined here
>            " %x ret %d", pos + sizeof(cap),
>              ~^
>              %lx

Ok, changed to %lx - which GCC version was that with? Didn't get any
warning with 6.3 on Debian 9.
Tiwei Bie Aug. 28, 2018, 6:47 a.m. | #3
On Mon, Aug 27, 2018 at 05:52:56PM +0100, Luca Boccassi wrote:
> On Mon, 2018-08-27 at 13:29 +0800, Tiwei Bie wrote:
> > On Fri, Aug 24, 2018 at 06:14:20PM +0100, Luca Boccassi wrote:
> > > From: Brian Russell <brussell@brocade.com>
> > > 
> > > In virtio_read_caps and vtpci_msix_detect, rte_pci_read_config
> > > returns
> > > the number of bytes read from PCI config or < 0 on error.
> > > If less than the expected number of bytes are read then log the
> > > failure and return rather than carrying on with garbage.
> > > 
> > > Fixes: 6ba1f63b5ab0 ("virtio: support specification 1.0")
> > > 
> > > Signed-off-by: Brian Russell <brussell@brocade.com>
> > > Signed-off-by: Luca Boccassi <bluca@debian.org>
> > > ---
> > > v2: handle additional rte_pci_read_config incomplete reads
> > > v3: do not handle rte_pci_read_config of virtio cap, added in v2,
> > >     as it's less clear what the right thing to do there is
> > > v4: do a more robust check - first check what the vendor is, and
> > >     skip the cap entirely if it's not what we are looking for.
> > > 
> > >  drivers/net/virtio/virtio_pci.c | 57 ++++++++++++++++++++++++-----
> > > ----
> > >  1 file changed, 42 insertions(+), 15 deletions(-)
> > > 
> > > diff --git a/drivers/net/virtio/virtio_pci.c
> > > b/drivers/net/virtio/virtio_pci.c
> > > index 6bd22e54a6..cfefa9789b 100644
> > > --- a/drivers/net/virtio/virtio_pci.c
> > > +++ b/drivers/net/virtio/virtio_pci.c
> > > @@ -567,16 +567,30 @@ virtio_read_caps(struct rte_pci_device *dev,
> > > struct virtio_hw *hw)
> > >  	}
> > >  
> > >  	ret = rte_pci_read_config(dev, &pos, 1,
> > > PCI_CAPABILITY_LIST);
> > > -	if (ret < 0) {
> > > -		PMD_INIT_LOG(DEBUG, "failed to read pci capability
> > > list");
> > > +	if (ret != 1) {
> > > +		PMD_INIT_LOG(DEBUG,
> > > +			     "failed to read pci capability list,
> > > ret %d", ret);
> > >  		return -1;
> > >  	}
> > >  
> > >  	while (pos) {
> > > +		ret = rte_pci_read_config(dev, &cap, 2, pos);
> > > +		if (ret != 2) {
> > > +			PMD_INIT_LOG(DEBUG,
> > > +				     "failed to read pci cap at
> > > pos: %x ret %d",
> > > +				     pos, ret);
> > > +			break;
> > > +		}
> > > +		if (cap.cap_vndr != PCI_CAP_ID_MSIX &&
> > > +				cap.cap_vndr != PCI_CAP_ID_VNDR) {
> > > +			goto next;
> > > +		}
> > > +
> > >  		ret = rte_pci_read_config(dev, &cap, sizeof(cap),
> > > pos);
> > > -		if (ret < 0) {
> > > -			PMD_INIT_LOG(ERR,
> > > -				"failed to read pci cap at pos:
> > > %x", pos);
> > > +		if (ret != sizeof(cap)) {
> > > +			PMD_INIT_LOG(DEBUG,
> > > +				     "failed to read pci cap at
> > > pos: %x ret %d",
> > > +				     pos, ret);
> > >  			break;
> > >  		}
> > >  
> > 
> > It seems that I didn't make myself clear in my previous
> > comments. I mean it's better to handle MSIX cap and virtio
> > cap respectively in this function. Currently we're always
> > reading them as virtio caps. As we are strictly requiring
> > that _read_config() should return the required number of
> > bytes, it's not perfect to require it to return "virtio
> > cap size" of bytes while we're trying to read a MSIX cap.
> > So please change the code to something similar to this:
> 
> Sorry, though you meant in the vtpci_msix_detect function, which I
> changed. Fixed in v5.

Thanks!

> 
> > > @@ -689,25 +703,38 @@ enum virtio_msix_status
> > >  vtpci_msix_detect(struct rte_pci_device *dev)
> > >  {
> > >  	uint8_t pos;
> > > -	struct virtio_pci_cap cap;
> > >  	int ret;
> > >  
> > >  	ret = rte_pci_read_config(dev, &pos, 1,
> > > PCI_CAPABILITY_LIST);
> > > -	if (ret < 0) {
> > > -		PMD_INIT_LOG(DEBUG, "failed to read pci capability
> > > list");
> > > +	if (ret != 1) {
> > > +		PMD_INIT_LOG(DEBUG,
> > > +			     "failed to read pci capability list,
> > > ret %d", ret);
> > >  		return VIRTIO_MSIX_NONE;
> > >  	}
> > >  
> > >  	while (pos) {
> > > -		ret = rte_pci_read_config(dev, &cap, sizeof(cap),
> > > pos);
> > > -		if (ret < 0) {
> > > -			PMD_INIT_LOG(ERR,
> > > -				"failed to read pci cap at pos:
> > > %x", pos);
> > > +		uint8_t cap[2];
> > > +
> > > +		ret = rte_pci_read_config(dev, cap, sizeof(cap),
> > > pos);
> > > +		if (ret != sizeof(cap)) {
> > > +			PMD_INIT_LOG(DEBUG,
> > > +				     "failed to read pci cap at
> > > pos: %x ret %d",
> > > +				     pos, ret);
> > >  			break;
> > >  		}
> > >  
> > > -		if (cap.cap_vndr == PCI_CAP_ID_MSIX) {
> > > -			uint16_t flags = ((uint16_t *)&cap)[1];
> > > +		if (cap[0] == PCI_CAP_ID_MSIX) {
> > > +			uint16_t flags;
> > > +
> > > +			ret = rte_pci_read_config(dev, &flags,
> > > sizeof(flags),
> > > +					pos + sizeof(cap));
> > > +			if (ret != sizeof(flags)) {
> > > +				PMD_INIT_LOG(DEBUG,
> > > +					     "failed to read pci
> > > cap at pos:"
> > > +					     " %x ret %d", pos +
> > > sizeof(cap),
> > 
> > There is a build error:
> > 
> > In file included from drivers/net/virtio/virtio_pci.c:15:
> > drivers/net/virtio/virtio_pci.c: In function ‘vtpci_msix_detect’:
> > drivers/net/virtio/virtio_logs.h:13:3: error: format ‘%x’ expects
> > argument of type ‘unsigned int’, but argument 5 has type ‘long
> > unsigned int’ [-Werror=format=]
> >    "%s(): " fmt "\n", __func__, ##args)
> >    ^~~~~~~~
> > drivers/net/virtio/virtio_pci.c:732:5: note: in expansion of macro
> > ‘PMD_INIT_LOG’
> >      PMD_INIT_LOG(DEBUG,
> >      ^~~~~~~~~~~~
> > drivers/net/virtio/virtio_pci.c:734:14: note: format string is
> > defined here
> >            " %x ret %d", pos + sizeof(cap),
> >              ~^
> >              %lx
> 
> Ok, changed to %lx - which GCC version was that with? Didn't get any
> warning with 6.3 on Debian 9.

I saw this with gcc (Debian 8.2.0-4) 8.2.0 on Debian sid.
I also saw similar warnings with clang version 6.0.0
(tags/RELEASE_600/final 326565) on FreeBSD 11.2

> 
> -- 
> Kind regards,
> Luca Boccassi

Patch

diff --git a/drivers/net/virtio/virtio_pci.c b/drivers/net/virtio/virtio_pci.c
index 6bd22e54a6..cfefa9789b 100644
--- a/drivers/net/virtio/virtio_pci.c
+++ b/drivers/net/virtio/virtio_pci.c
@@ -567,16 +567,30 @@  virtio_read_caps(struct rte_pci_device *dev, struct virtio_hw *hw)
 	}
 
 	ret = rte_pci_read_config(dev, &pos, 1, PCI_CAPABILITY_LIST);
-	if (ret < 0) {
-		PMD_INIT_LOG(DEBUG, "failed to read pci capability list");
+	if (ret != 1) {
+		PMD_INIT_LOG(DEBUG,
+			     "failed to read pci capability list, ret %d", ret);
 		return -1;
 	}
 
 	while (pos) {
+		ret = rte_pci_read_config(dev, &cap, 2, pos);
+		if (ret != 2) {
+			PMD_INIT_LOG(DEBUG,
+				     "failed to read pci cap at pos: %x ret %d",
+				     pos, ret);
+			break;
+		}
+		if (cap.cap_vndr != PCI_CAP_ID_MSIX &&
+				cap.cap_vndr != PCI_CAP_ID_VNDR) {
+			goto next;
+		}
+
 		ret = rte_pci_read_config(dev, &cap, sizeof(cap), pos);
-		if (ret < 0) {
-			PMD_INIT_LOG(ERR,
-				"failed to read pci cap at pos: %x", pos);
+		if (ret != sizeof(cap)) {
+			PMD_INIT_LOG(DEBUG,
+				     "failed to read pci cap at pos: %x ret %d",
+				     pos, ret);
 			break;
 		}
 
@@ -689,25 +703,38 @@  enum virtio_msix_status
 vtpci_msix_detect(struct rte_pci_device *dev)
 {
 	uint8_t pos;
-	struct virtio_pci_cap cap;
 	int ret;
 
 	ret = rte_pci_read_config(dev, &pos, 1, PCI_CAPABILITY_LIST);
-	if (ret < 0) {
-		PMD_INIT_LOG(DEBUG, "failed to read pci capability list");
+	if (ret != 1) {
+		PMD_INIT_LOG(DEBUG,
+			     "failed to read pci capability list, ret %d", ret);
 		return VIRTIO_MSIX_NONE;
 	}
 
 	while (pos) {
-		ret = rte_pci_read_config(dev, &cap, sizeof(cap), pos);
-		if (ret < 0) {
-			PMD_INIT_LOG(ERR,
-				"failed to read pci cap at pos: %x", pos);
+		uint8_t cap[2];
+
+		ret = rte_pci_read_config(dev, cap, sizeof(cap), pos);
+		if (ret != sizeof(cap)) {
+			PMD_INIT_LOG(DEBUG,
+				     "failed to read pci cap at pos: %x ret %d",
+				     pos, ret);
 			break;
 		}
 
-		if (cap.cap_vndr == PCI_CAP_ID_MSIX) {
-			uint16_t flags = ((uint16_t *)&cap)[1];
+		if (cap[0] == PCI_CAP_ID_MSIX) {
+			uint16_t flags;
+
+			ret = rte_pci_read_config(dev, &flags, sizeof(flags),
+					pos + sizeof(cap));
+			if (ret != sizeof(flags)) {
+				PMD_INIT_LOG(DEBUG,
+					     "failed to read pci cap at pos:"
+					     " %x ret %d", pos + sizeof(cap),
+					     ret);
+				break;
+			}
 
 			if (flags & PCI_MSIX_ENABLE)
 				return VIRTIO_MSIX_ENABLED;
@@ -715,7 +742,7 @@  vtpci_msix_detect(struct rte_pci_device *dev)
 				return VIRTIO_MSIX_DISABLED;
 		}
 
-		pos = cap.cap_next;
+		pos = cap[1];
 	}
 
 	return VIRTIO_MSIX_NONE;