linux-kernel - Re: [PATCH v3 4/4] vdpa/octeon_ep: read vendor-specific PCI capability

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Message-ID:
 <PH0PR18MB4425608D09BF3BFD4C551D0AD9392@PH0PR18MB4425.namprd18.prod.outlook.com>
Date: Sat, 14 Dec 2024 06:29:19 +0000
From: Shijith Thotton <sthotton@...vell.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: Jason Wang <jasowang@...hat.com>,
        "virtualization@...ts.linux.dev"
	<virtualization@...ts.linux.dev>,
        "dan.carpenter@...aro.org"
	<dan.carpenter@...aro.org>,
        Srujana Challa <schalla@...vell.com>,
        Vamsi
 Krishna Attunuru <vattunuru@...vell.com>,
        Nithin Kumar Dabilpuram
	<ndabilpuram@...vell.com>,
        Jerin Jacob <jerinj@...vell.com>,
        Xuan Zhuo
	<xuanzhuo@...ux.alibaba.com>,
        Eugenio Pérez
	<eperezma@...hat.com>,
        Satha Koteswara Rao Kottidi <skoteshwar@...vell.com>,
        open list <linux-kernel@...r.kernel.org>,
        Shijith Thotton
	<sthotton@...vell.com>
Subject: Re: [PATCH v3 4/4] vdpa/octeon_ep: read vendor-specific PCI
 capability

>> >>> Added support to read the vendor-specific PCI capability to identify the
>> >>> type of device being emulated.
>> >>>
>> >>> Reviewed-by: Dan Carpenter <dan.carpenter@...aro.org>
>> >>> Signed-off-by: Shijith Thotton <sthotton@...vell.com>
>> >>> ---
>> >>>  drivers/vdpa/octeon_ep/octep_vdpa.h      | 20 ++++++++++++++
>> >>>  drivers/vdpa/octeon_ep/octep_vdpa_hw.c   | 33
>> >>+++++++++++++++++++++++-
>> >>>  drivers/vdpa/octeon_ep/octep_vdpa_main.c |  4 ++-
>> >>>  3 files changed, 55 insertions(+), 2 deletions(-)
>> >>>
>> >>> diff --git a/drivers/vdpa/octeon_ep/octep_vdpa.h
>> >>b/drivers/vdpa/octeon_ep/octep_vdpa.h
>> >>> index 2cadb878e679..53b020b019f7 100644
>> >>> --- a/drivers/vdpa/octeon_ep/octep_vdpa.h
>> >>> +++ b/drivers/vdpa/octeon_ep/octep_vdpa.h
>> >>> @@ -8,6 +8,7 @@
>> >>>  #include <linux/pci_regs.h>
>> >>>  #include <linux/vdpa.h>
>> >>>  #include <linux/virtio_pci_modern.h>
>> >>> +#include <uapi/linux/virtio_crypto.h>
>> >>>  #include <uapi/linux/virtio_net.h>
>> >>>  #include <uapi/linux/virtio_blk.h>
>> >>>  #include <uapi/linux/virtio_config.h>
>> >>> @@ -52,6 +53,24 @@ struct octep_vring_info {
>> >>>         phys_addr_t notify_pa;
>> >>>  };
>> >>>
>> >>> +enum octep_pci_vndr_cfg_type {
>> >>> +       OCTEP_PCI_VNDR_CFG_TYPE_VIRTIO_ID,
>> >>> +       OCTEP_PCI_VNDR_CFG_TYPE_MAX,
>> >>> +};
>> >>> +
>> >>> +struct octep_pci_vndr_data {
>> >>> +       struct virtio_pci_vndr_data hdr;
>> >>> +       u8 id;
>> >>> +       u8 bar;
>> >>> +       union {
>> >>> +               u64 data;
>> >>> +               struct {
>> >>> +                       u32 offset;
>> >>> +                       u32 length;
>> >>> +               };
>> >>> +       };
>> >>> +};
>> >>
>> >>This seems not to be padded to a multiple of 4 bytes?
>> >>
>> >
>> >Looks like, the structure is naturally aligned.
>> >
>> >struct virtio_pci_vndr_data {
>> >        uint8_t                    cap_vndr;             /*     0     1 */
>> >        uint8_t                    cap_next;             /*     1     1 */
>> >        uint8_t                    cap_len;              /*     2     1 */
>> >        uint8_t                    cfg_type;             /*     3     1 */
>> >        uint16_t                   vendor_id;            /*     4     2 */
>> >        /* size: 6, cachelines: 1, members: 5 */
>> >        /* last cacheline: 6 bytes */
>> >};
>> >struct octep_pci_vndr_data {
>> >        struct virtio_pci_vndr_data hdr;                 /*     0     6 */
>> >        uint8_t                    id;                   /*     6     1 */
>> >        uint8_t                    bar;                  /*     7     1 */
>> >        union {
>> >                uint64_t           data;                 /*     8     8 */
>> >                struct {
>> >                        uint32_t   offset;               /*     8     4 */
>> >                        uint32_t   length;               /*    12     4 */
>> >                };                                       /*     8     8 */
>> >        };                                               /*     8     8 */
>> >
>> >        /* size: 16, cachelines: 1, members: 4 */
>> >        /* last cacheline: 16 bytes */
>> >};
>> >
>> >I will add __attribute__((aligned(4))) to be safe.
>> >
>>
>> Small correction, I meant   __attribute__((packed, aligned(4))).
>>
>> Thanks,
>> Shijith
>
>Don't add packed pls, for me it means "something is not packed naturally
>here". when in fact it is.
>
>aligned is also bad, since it can add padding which creates all
>kind of security issues.
>
>If you want to be sure, add BUILD_BUG_ON and check that it is aligned
>as expected.

Sure, I will use BUILD_BUG_ON to check the structure size.
BUILD_BUG_ON(sizeof(struct octep_pci_vndr_data) % 4 != 0);

Thanks,
Shijith