Re: [PATCH v5] vpci: Add resizable bar support

["Roger Pau Monné" <roger.pau@citrix.com>]

On Tue, Jan 14, 2025 at 11:26:36AM +0800, Jiqian Chen wrote:
> Some devices, like discrete GPU of amd, support resizable bar
> capability, but vpci of Xen doesn't support this feature, so
> they fail to resize bars and then cause probing failure.
> 
> According to PCIe spec, each bar that supports resizing has
> two registers, PCI_REBAR_CAP and PCI_REBAR_CTRL. So, add
> handlers for them to support resizing the size of BARs.
> 
> Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
> ---
> Hi all,
> v4->v5 changes:
> * Called pci_size_mem_bar in rebar_ctrl_write to get addr and size of BAR instead of setting
>   their values directly after writing new size to hardware.
> * Changed from "return" to "continue" when index/type of BAR are not correct during initializing
>   BAR.
> * Corrected the value of PCI_REBAR_CTRL_BAR_SIZE from "0x00001F00" to "0x00003F00".
> * Renamed PCI_REBAR_SIZE_BIAS to PCI_REBAR_CTRL_SIZE_BIAS.
> * Re-defined "PCI_REBAR_CAP_SHIFT 4" to "PCI_REBAR_CAP_SIZES_MASK 0xFFFFFFF0U".
> 
> Best regards,
> Jiqian Chen.
> 
> v3->v4 changes:
> * Removed PCI_REBAR_CAP_SIZES since it was not needed, and added
>   PCI_REBAR_CAP_SHIFT and PCI_REBAR_CTRL_SIZES.
> * Added parameter resizable_sizes to struct vpci_bar to cache the support resizable sizes and
>   added the logic in init_rebar().
> * Changed PCI_REBAR_CAP to PCI_REBAR_CAP(n) (4+8*(n)), changed PCI_REBAR_CTRL to
>   PCI_REBAR_CTRL(n) (8+8*(n)).
> * Added domain info of pci_dev to printings of init_rebar().
> 
> v2->v3 changes:
> * Used "bar->enabled" to replace "pci_conf_read16(pdev->sbdf, PCI_COMMAND) & PCI_COMMAND_MEMORY",
>   and added comments why it needs this check.
> * Added "!is_hardware_domain(pdev->domain)" check in init_rebar() to return EOPNOTSUPP for domUs.
> * Moved BAR type and index check into init_rebar(), then only need to check once.
> * Added 'U' suffix for macro PCI_REBAR_CAP_SIZES.
> * Added macro PCI_REBAR_SIZE_BIAS to represent 20.
> TODO: need to hide ReBar capability from hardware domain when init_rebar() fails.
> 
> v1->v2 changes:
> * In rebar_ctrl_write, to check if memory decoding is enabled, and added
>   some checks for the type of Bar.
> * Added vpci_hw_write32 to handle PCI_REBAR_CAP's write, since there is
>   no write limitation of dom0.
> * And has many other minor modifications as well.
> ---
>  xen/drivers/vpci/Makefile  |   2 +-
>  xen/drivers/vpci/rebar.c   | 135 +++++++++++++++++++++++++++++++++++++
>  xen/drivers/vpci/vpci.c    |   6 ++
>  xen/include/xen/pci_regs.h |  14 ++++
>  xen/include/xen/vpci.h     |   3 +
>  5 files changed, 159 insertions(+), 1 deletion(-)
>  create mode 100644 xen/drivers/vpci/rebar.c
> 
> diff --git a/xen/drivers/vpci/Makefile b/xen/drivers/vpci/Makefile
> index 1a1413b93e76..a7c8a30a8956 100644
> --- a/xen/drivers/vpci/Makefile
> +++ b/xen/drivers/vpci/Makefile
> @@ -1,2 +1,2 @@
> -obj-y += vpci.o header.o
> +obj-y += vpci.o header.o rebar.o
>  obj-$(CONFIG_HAS_PCI_MSI) += msi.o msix.o
> diff --git a/xen/drivers/vpci/rebar.c b/xen/drivers/vpci/rebar.c
> new file mode 100644
> index 000000000000..ed22a75e16fd
> --- /dev/null
> +++ b/xen/drivers/vpci/rebar.c
> @@ -0,0 +1,135 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2024 Advanced Micro Devices, Inc. All Rights Reserved.
> + *
> + * Author: Jiqian Chen <Jiqian.Chen@amd.com>
> + */
> +
> +#include <xen/sched.h>
> +#include <xen/vpci.h>
> +
> +static void cf_check rebar_ctrl_write(const struct pci_dev *pdev,
> +                                      unsigned int reg,
> +                                      uint32_t val,
> +                                      void *data)
> +{
> +    unsigned int index;
> +    struct vpci_bar *bar = data;
> +    uint64_t size = PCI_REBAR_CTRL_SIZE(val);
> +
> +    if ( bar->enabled )
> +    {
> +        /*
> +         * Refuse to resize a BAR while memory decoding is enabled, as
> +         * otherwise the size of the mapped region in the p2m would become
> +         * stale with the newly set BAR size, and the position of the BAR
> +         * would be reset to undefined.  Note the PCIe specification also
> +         * forbids resizing a BAR with memory decoding enabled.
> +         */
> +        if ( size != bar->size )
> +            gprintk(XENLOG_ERR,
> +                    "%pp: refuse to resize BAR with memory decoding enabled\n",
> +                    &pdev->sbdf);
> +        return;
> +    }
> +
> +    if ( !((size >> PCI_REBAR_CTRL_SIZE_BIAS) & bar->resizable_sizes) )
> +        gprintk(XENLOG_WARNING,
> +                "%pp: new size %#lx is not supported by hardware\n",
> +                &pdev->sbdf, size);
> +
> +    pci_conf_write32(pdev->sbdf, reg, val);
> +
> +    index = pci_conf_read32(pdev->sbdf, reg) & PCI_REBAR_CTRL_BAR_IDX;

No need for the PCI config space access, you can get the index using:

bar - pdev->vpci->header.bars

In fact you could define the local variables as:

struct vpci_bar *bar = data;
const unsigned int index = bar - pdev->vpci->header.bars;
uint64_t size = PCI_REBAR_CTRL_SIZE(val);

And use index in the error messages also:

"%pp: refuse to resize BAR#u with memory decoding enabled\n"
"%pp: new BAR#%u size %#lx is not supported by hardware\n",

> +    pci_size_mem_bar(pdev->sbdf, PCI_BASE_ADDRESS_0 + index * 4, &bar->addr,
> +                     &bar->size, ((index == PCI_HEADER_NORMAL_NR_BARS - 1) ?
> +                                  PCI_BAR_LAST : 0));

Seeing as Jan already asked you to fix indentation here, I think you
can also drop the outermost parentheses from the last argument.

> +    bar->guest_addr = bar->addr;
> +}
> +
> +static int cf_check init_rebar(struct pci_dev *pdev)
> +{
> +    uint32_t ctrl;
> +    unsigned int nbars;
> +    unsigned int rebar_offset = pci_find_ext_capability(pdev->sbdf,
> +                                                        PCI_EXT_CAP_ID_REBAR);
> +
> +    if ( !rebar_offset )
> +        return 0;
> +
> +    if ( !is_hardware_domain(pdev->domain) )
> +    {
> +        printk(XENLOG_ERR "%pp: resizable BARs unsupported for unpriv %pd\n",
> +               &pdev->sbdf, pdev->domain);
> +        return -EOPNOTSUPP;
> +    }
> +
> +    ctrl = pci_conf_read32(pdev->sbdf, rebar_offset + PCI_REBAR_CTRL(0));
> +    nbars = MASK_EXTR(ctrl, PCI_REBAR_CTRL_NBAR_MASK);
> +    for ( unsigned int i = 0; i < nbars; i++ )
> +    {
> +        int rc;
> +        struct vpci_bar *bar;
> +        unsigned int index;
> +
> +        ctrl = pci_conf_read32(pdev->sbdf, rebar_offset + PCI_REBAR_CTRL(i));
> +        index = ctrl & PCI_REBAR_CTRL_BAR_IDX;
> +        if ( index >= PCI_HEADER_NORMAL_NR_BARS )
> +        {
> +            printk(XENLOG_ERR "%pd %pp: too big BAR number %u in REBAR_CTRL\n",
> +                   pdev->domain, &pdev->sbdf, index);
> +            continue;
> +        }
> +
> +        bar = &pdev->vpci->header.bars[index];
> +        if ( bar->type != VPCI_BAR_MEM64_LO && bar->type != VPCI_BAR_MEM32 )
> +        {
> +            printk(XENLOG_ERR "%pd %pp: BAR%u is not in memory space\n",
> +                   pdev->domain, &pdev->sbdf, index);
> +            continue;
> +        }
> +
> +        rc = vpci_add_register(pdev->vpci, vpci_hw_read32, vpci_hw_write32,
> +                               rebar_offset + PCI_REBAR_CAP(i), 4, NULL);
> +        if ( rc )
> +        {
> +            /*
> +             * TODO: for failed pathes, need to hide ReBar capability
> +             * from hardware domain instead of returning an error.
> +             */
> +            printk(XENLOG_ERR "%pd %pp: fail to add reg of REBAR_CAP rc=%d\n",
> +                   pdev->domain, &pdev->sbdf, rc);
> +            return rc;
> +        }
> +
> +        rc = vpci_add_register(pdev->vpci, vpci_hw_read32, rebar_ctrl_write,
> +                               rebar_offset + PCI_REBAR_CTRL(i), 4, bar);
> +        if ( rc )
> +        {
> +            printk(XENLOG_ERR "%pd %pp: fail to add reg of REBAR_CTRL rc=%d\n",
> +                   pdev->domain, &pdev->sbdf, rc);
> +            return rc;

I think we said we wanted to attempt to continue here, rather than
returning an error and thus removing all vPCI handlers from the
device?

Error messages should also contain the BAR index IMO:

"%pd %pp: BAR%u fail to add reg of REBAR_{CAP,CTRL} rc=%d\n"

Thanks, Roger.