[PATCH v8] vpci: Add resizable bar support

[Jiqian Chen <Jiqian.Chen@xxxxxxx>]

Some devices, like AMDGPU, 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 to support resizing the size of BARs.

Note that Xen will only trap PCI_REBAR_CTRL, as PCI_REBAR_CAP
is read-only register and the hardware domain already gets
access to it without needing any setup.

Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
---
Hi all,
v7->v8 changes:
* Modified commit message and some comments.
* Deleted unused function vpci_hw_write32.

Best regards,
Jiqian Chen.

v6->v7 changes:
* Deleted codes that add register for PCI_REBAR_CAP, and added comments to 
explain why.
* Added comments to explain why use "continue" when fail to add register for 
PCI_REBAR_CTRL.

v5->v6 changes:
* Changed "1UL" to "1ULL" in PCI_REBAR_CTRL_SIZE idefinition for 32 bit 
architecture.
* In rebar_ctrl_write used "bar - pdev->vpci->header.bars" to get index instead 
of reading
  from register.
* Added the index of BAR to error messages.
* Changed to "continue" instead of "return an error" when vpci_add_register 
failed.

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".

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   | 131 +++++++++++++++++++++++++++++++++++++
 xen/include/xen/pci_regs.h |  15 +++++
 xen/include/xen/vpci.h     |   1 +
 4 files changed, 148 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..794f1168adf8
--- /dev/null
+++ b/xen/drivers/vpci/rebar.c
@@ -0,0 +1,131 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2025 Advanced Micro Devices, Inc. All Rights Reserved.
+ *
+ * Author: Jiqian Chen <Jiqian.Chen@xxxxxxx>
+ */
+
+#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)
+{
+    struct vpci_bar *bar = data;
+    const unsigned int index = bar - pdev->vpci->header.bars;
+    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#%u with memory decoding 
enabled\n",
+                    &pdev->sbdf, index);
+        return;
+    }
+
+    if ( !((size >> PCI_REBAR_CTRL_SIZE_BIAS) & bar->resizable_sizes) )
+        gprintk(XENLOG_WARNING,
+                "%pp: new BAR#%u size %#lx is not supported by hardware\n",
+                &pdev->sbdf, index, size);
+
+    pci_conf_write32(pdev->sbdf, reg, val);
+
+    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);
+    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, rebar_ctrl_write,
+                               rebar_offset + PCI_REBAR_CTRL(i), 4, bar);
+        if ( rc )
+        {
+            printk(XENLOG_ERR "%pd %pp: BAR%u fail to add reg of REBAR_CTRL 
rc=%d\n",
+                   pdev->domain, &pdev->sbdf, index, rc);
+            /*
+             * Ideally we would hide the ReBar capability on error, but code
+             * for doing so still needs to be written. Use continue instead
+             * to keep any already setup register hooks, as returning an
+             * error will cause the hardware domain to get unmediated access
+             * to all device registers.
+             */
+            continue;
+        }
+
+        bar->resizable_sizes =
+            MASK_EXTR(pci_conf_read32(pdev->sbdf,
+                                      rebar_offset + PCI_REBAR_CAP(i)),
+                      PCI_REBAR_CAP_SIZES_MASK);
+        bar->resizable_sizes |=
+            (((uint64_t)MASK_EXTR(ctrl, PCI_REBAR_CTRL_SIZES_MASK) << 32) /
+             ISOLATE_LSB(PCI_REBAR_CAP_SIZES_MASK));
+    }
+
+    return 0;
+}
+REGISTER_VPCI_INIT(init_rebar, VPCI_PRIORITY_LOW);
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/include/xen/pci_regs.h b/xen/include/xen/pci_regs.h
index 250ba106dbd3..2f1d0d63e962 100644
--- a/xen/include/xen/pci_regs.h
+++ b/xen/include/xen/pci_regs.h
@@ -459,6 +459,7 @@
 #define PCI_EXT_CAP_ID_ARI     14
 #define PCI_EXT_CAP_ID_ATS     15
 #define PCI_EXT_CAP_ID_SRIOV   16
+#define PCI_EXT_CAP_ID_REBAR   21      /* Resizable BAR */
 
 /* Advanced Error Reporting */
 #define PCI_ERR_UNCOR_STATUS   4       /* Uncorrectable Error Status */
@@ -541,6 +542,20 @@
 #define  PCI_VNDR_HEADER_REV(x)        (((x) >> 16) & 0xf)
 #define  PCI_VNDR_HEADER_LEN(x)        (((x) >> 20) & 0xfff)
 
+/* Resizable BARs */
+#define PCI_REBAR_CAP(n)       (4 + 8 * (n))   /* capability register */
+#define  PCI_REBAR_CAP_SIZES_MASK      0xFFFFFFF0U     /* supported BAR sizes 
in CAP */
+#define PCI_REBAR_CTRL(n)      (8 + 8 * (n))   /* control register */
+#define  PCI_REBAR_CTRL_BAR_IDX                0x00000007      /* BAR index */
+#define  PCI_REBAR_CTRL_NBAR_MASK      0x000000E0      /* # of resizable BARs 
*/
+#define  PCI_REBAR_CTRL_BAR_SIZE       0x00003F00      /* BAR size */
+#define  PCI_REBAR_CTRL_SIZES_MASK     0xFFFF0000U     /* supported BAR sizes 
in CTRL */
+
+#define PCI_REBAR_CTRL_SIZE_BIAS       20
+#define PCI_REBAR_CTRL_SIZE(v) \
+            (1ULL << (MASK_EXTR(v, PCI_REBAR_CTRL_BAR_SIZE) \
+                      + PCI_REBAR_CTRL_SIZE_BIAS))
+
 /*
  * Hypertransport sub capability types
  *
diff --git a/xen/include/xen/vpci.h b/xen/include/xen/vpci.h
index 41e7c3bc2791..807401b2eaa2 100644
--- a/xen/include/xen/vpci.h
+++ b/xen/include/xen/vpci.h
@@ -100,6 +100,7 @@ struct vpci {
             /* Guest address. */
             uint64_t guest_addr;
             uint64_t size;
+            uint64_t resizable_sizes;
             struct rangeset *mem;
             enum {
                 VPCI_BAR_EMPTY,
-- 
2.34.1