Re: [PATCH v4 2/9] cxl/mem: Find device capabilities

Ben Widawsky
2021-02-16T17:56:09Z

On 21-02-16 17:20:01, Jonathan Cameron wrote:
> On Tue, 16 Feb 2021 08:43:03 -0800
> Ben Widawsky <ben.widawsky@intel.com> wrote:
>
> > On 21-02-16 14:51:48, Jonathan Cameron wrote:
> > > On Mon, 15 Feb 2021 17:45:31 -0800
> > > Ben Widawsky <ben.widawsky@intel.com> wrote:
> > >
> > > > Provide enough functionality to utilize the mailbox of a memory device.
> > > > The mailbox is used to interact with the firmware running on the memory
> > > > device. The flow is proven with one implemented command, "identify".
> > > > Because the class code has already told the driver this is a memory
> > > > device and the identify command is mandatory.
> > > >
> > > > CXL devices contain an array of capabilities that describe the
> > > > interactions software can have with the device or firmware running on
> > > > the device. A CXL compliant device must implement the device status and
> > > > the mailbox capability. Additionally, a CXL compliant memory device must
> > > > implement the memory device capability. Each of the capabilities can
> > > > [will] provide an offset within the MMIO region for interacting with the
> > > > CXL device.
> > > >
> > > > The capabilities tell the driver how to find and map the register space
> > > > for CXL Memory Devices. The registers are required to utilize the CXL
> > > > spec defined mailbox interface. The spec outlines two mailboxes, primary
> > > > and secondary. The secondary mailbox is earmarked for system firmware,
> > > > and not handled in this driver.
> > > >
> > > > Primary mailboxes are capable of generating an interrupt when submitting
> > > > a background command. That implementation is saved for a later time.
> > > >
> > > > Link: https://www.computeexpresslink.org/download-the-specification
> > > > Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> > > > Reviewed-by: Dan Williams <dan.j.williams@intel.com> (v2)
> > >
> > > Looks like an off by one error in the register locator iteration.
> > >
> > > The potential buffer overrun from memcpy_fromio is still there as well
> > > as far as I can see.
> > >
> > > If the software provides storage for a payload of size n and the hardware
> > > reports a size of n + d, code will happily write beyond the end of the
> > > storage provided.
> > >
> > > Obviously, this shouldn't happen, but I'm not that trusting of both
> > > hardware and software never having bugs.
> > >
> > > Jonathan
> > >
> > > > ---
> > > > drivers/cxl/cxl.h | 88 ++++++++
> > > > drivers/cxl/mem.c | 543 +++++++++++++++++++++++++++++++++++++++++++++-
> > > > drivers/cxl/pci.h | 14 ++
> > > > 3 files changed, 643 insertions(+), 2 deletions(-)
> > > > create mode 100644 drivers/cxl/cxl.h
> > > >
> > > ...
> > >
> > > > +
> > > > +#endif /* __CXL_H__ */
> > > > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> > > > index ce33c5ee77c9..b86cda2d299a 100644
> > > > --- a/drivers/cxl/mem.c
> > > > +++ b/drivers/cxl/mem.c
> > > > @@ -3,7 +3,458 @@
> > > > #include <linux/module.h>
> > > > #include <linux/pci.h>
> > > > #include <linux/io.h>
> > > > +#include <linux/io-64-nonatomic-lo-hi.h>
> > > > #include "pci.h"
> > > > +#include "cxl.h"
> > > > +
> > > > +#define cxl_doorbell_busy(cxlm) \
> > > > + (readl((cxlm)->mbox_regs + CXLDEV_MBOX_CTRL_OFFSET) & \
> > > > + CXLDEV_MBOX_CTRL_DOORBELL)
> > > > +
> > > > +/* CXL 2.0 - 8.2.8.4 */
> > > > +#define CXL_MAILBOX_TIMEOUT_MS (2 * HZ)
> > > > +
> > > > +enum opcode {
> > > > + CXL_MBOX_OP_IDENTIFY = 0x4000,
> > > > + CXL_MBOX_OP_MAX = 0x10000
> > > > +};
> > > > +
> > > > +/**
> > > > + * struct mbox_cmd - A command to be submitted to hardware.
> > > > + * @opcode: (input) The command set and command submitted to hardware.
> > > > + * @payload_in: (input) Pointer to the input payload.
> > > > + * @payload_out: (output) Pointer to the output payload. Must be allocated by
> > > > + * the caller.
> > > > + * @size_in: (input) Number of bytes to load from @payload.
> > > > + * @size_out: (output) Number of bytes loaded into @payload.
> > > > + * @return_code: (output) Error code returned from hardware.
> > > > + *
> > > > + * This is the primary mechanism used to send commands to the hardware.
> > > > + * All the fields except @payload_* correspond exactly to the fields described in
> > > > + * Command Register section of the CXL 2.0 8.2.8.4.5. @payload_in and
> > > > + * @payload_out are written to, and read from the Command Payload Registers
> > > > + * defined in CXL 2.0 8.2.8.4.8.
> > > > + */
> > > > +struct mbox_cmd {
> > > > + u16 opcode;
> > > > + void *payload_in;
> > > > + void *payload_out;
> > > > + size_t size_in;
> > > > + size_t size_out;
> > > > + u16 return_code;
> > > > +#define CXL_MBOX_SUCCESS 0
> > > > +};
> > >
> > >
> > > > +
> > > > +/**
> > > > + * __cxl_mem_mbox_send_cmd() - Execute a mailbox command
> > > > + * @cxlm: The CXL memory device to communicate with.
> > > > + * @mbox_cmd: Command to send to the memory device.
> > > > + *
> > > > + * Context: Any context. Expects mbox_mutex to be held.
> > > > + * Return: -ETIMEDOUT if timeout occurred waiting for completion. 0 on success.
> > > > + * Caller should check the return code in @mbox_cmd to make sure it
> > > > + * succeeded.
> > > > + *
> > > > + * This is a generic form of the CXL mailbox send command thus only using the
> > > > + * registers defined by the mailbox capability ID - CXL 2.0 8.2.8.4. Memory
> > > > + * devices, and perhaps other types of CXL devices may have further information
> > > > + * available upon error conditions. Driver facilities wishing to send mailbox
> > > > + * commands should use the wrapper command.
> > > > + *
> > > > + * The CXL spec allows for up to two mailboxes. The intention is for the primary
> > > > + * mailbox to be OS controlled and the secondary mailbox to be used by system
> > > > + * firmware. This allows the OS and firmware to communicate with the device and
> > > > + * not need to coordinate with each other. The driver only uses the primary
> > > > + * mailbox.
> > > > + */
> > > > +static int __cxl_mem_mbox_send_cmd(struct cxl_mem *cxlm,
> > > > + struct mbox_cmd *mbox_cmd)
> > > > +{
> > > > + void __iomem *payload = cxlm->mbox_regs + CXLDEV_MBOX_PAYLOAD_OFFSET;
> > > > + u64 cmd_reg, status_reg;
> > > > + size_t out_len;
> > > > + int rc;
> > > > +
> > > > + lockdep_assert_held(&cxlm->mbox_mutex);
> > > > +
> > > > + /*
> > > > + * Here are the steps from 8.2.8.4 of the CXL 2.0 spec.
> > > > + * 1. Caller reads MB Control Register to verify doorbell is clear
> > > > + * 2. Caller writes Command Register
> > > > + * 3. Caller writes Command Payload Registers if input payload is non-empty
> > > > + * 4. Caller writes MB Control Register to set doorbell
> > > > + * 5. Caller either polls for doorbell to be clear or waits for interrupt if configured
> > > > + * 6. Caller reads MB Status Register to fetch Return code
> > > > + * 7. If command successful, Caller reads Command Register to get Payload Length
> > > > + * 8. If output payload is non-empty, host reads Command Payload Registers
> > > > + *
> > > > + * Hardware is free to do whatever it wants before the doorbell is rung,
> > > > + * and isn't allowed to change anything after it clears the doorbell. As
> > > > + * such, steps 2 and 3 can happen in any order, and steps 6, 7, 8 can
> > > > + * also happen in any order (though some orders might not make sense).
> > > > + */
> > > > +
> > > > + /* #1 */
> > > > + if (cxl_doorbell_busy(cxlm)) {
> > > > + dev_err_ratelimited(&cxlm->pdev->dev,
> > > > + "Mailbox re-busy after acquiring\n");
> > > > + return -EBUSY;
> > > > + }
> > > > +
> > > > + cmd_reg = FIELD_PREP(CXLDEV_MBOX_CMD_COMMAND_OPCODE_MASK,
> > > > + mbox_cmd->opcode);
> > > > + if (mbox_cmd->size_in) {
> > > > + if (WARN_ON(!mbox_cmd->payload_in))
> > > > + return -EINVAL;
> > > > +
> > > > + cmd_reg |= FIELD_PREP(CXLDEV_MBOX_CMD_PAYLOAD_LENGTH_MASK,
> > > > + mbox_cmd->size_in);
> > > > + memcpy_toio(payload, mbox_cmd->payload_in, mbox_cmd->size_in);
> > > > + }
> > > > +
> > > > + /* #2, #3 */
> > > > + writeq(cmd_reg, cxlm->mbox_regs + CXLDEV_MBOX_CMD_OFFSET);
> > > > +
> > > > + /* #4 */
> > > > + dev_dbg(&cxlm->pdev->dev, "Sending command\n");
> > > > + writel(CXLDEV_MBOX_CTRL_DOORBELL,
> > > > + cxlm->mbox_regs + CXLDEV_MBOX_CTRL_OFFSET);
> > > > +
> > > > + /* #5 */
> > > > + rc = cxl_mem_wait_for_doorbell(cxlm);
> > > > + if (rc == -ETIMEDOUT) {
> > > > + cxl_mem_mbox_timeout(cxlm, mbox_cmd);
> > > > + return rc;
> > > > + }
> > > > +
> > > > + /* #6 */
> > > > + status_reg = readq(cxlm->mbox_regs + CXLDEV_MBOX_STATUS_OFFSET);
> > > > + mbox_cmd->return_code =
> > > > + FIELD_GET(CXLDEV_MBOX_STATUS_RET_CODE_MASK, status_reg);
> > > > +
> > > > + if (mbox_cmd->return_code != 0) {
> > > > + dev_dbg(&cxlm->pdev->dev, "Mailbox operation had an error\n");
> > > > + return 0;
> > > > + }
> > > > +
> > > > + /* #7 */
> > > > + cmd_reg = readq(cxlm->mbox_regs + CXLDEV_MBOX_CMD_OFFSET);
> > > > + out_len = FIELD_GET(CXLDEV_MBOX_CMD_PAYLOAD_LENGTH_MASK, cmd_reg);
> > > > +
> > > > + /* #8 */
> > > > + if (out_len && mbox_cmd->payload_out) {
> > > > + size_t n = min_t(size_t, cxlm->payload_size, out_len);
> > >
> > > This doesn't protect us from the case where the hardware
> > > returns a larger payload than the caller is expecting.
> > >
> > > i.e. payload_out is too small. We need to pass in the size of that buffer as
> > > well. This currently clamps to the size of the source buffer but does not
> > > check if there is enough space at the destination (mbox_cmd->payload_out).
> > >
> >
> > Let me articulate the issue a bit. The userspace call chain should be fine:
> > cxl_send_cmd() -> ioctl handlers
> > cxl_validate_cmd_from_user -> converts to internal command
> > handle_mailbox_cmd_from_user -> dispatches mbox command.
>
> There is a sanity check in there against info->size_out, that will return
> an error if the buffer isn't big enough. However, that test passes
> for a variable length command. It is then followed by
>
> out_cmd->info.size_out = send_cmd->out.size;
> (perhaps that is meant to be = info->size_out so as to pick up the -1?)
>
> handle_mailbox_cmd_from_user() then uses that size in
> mbox_cmd.payload_out = kvzalloc(cmd->info.size_out, GFP_KERNEL);
>
> >
> > cxl_send_cmd():
> > if (c.info.size_out < 0)
> > c.info.size_out = cxlm->payload_size;
> >
> (c == out_cmd above)
> So this doesn't apply because c.info.size_out is whatever userspace set it to.
>
> > handle_mailbox_cmd_from_user():
> > if (cmd->info.size_out) {
> > mbox_cmd.payload_out = kvzalloc(cmd->info.size_out, GFP_KERNEL);
>
> __cxl_mem_mbox_send_cmd() called with that payload size and blindly
> copies whatever size of data the hardware receives into the the buffer we allocated
> above. If it's not big enough you now have a userspace triggered buffer overflow in
> the kernel.
> All userspace needs to do is issue an ioctl for a raw command with the out.size
> set too small but not set to -1.

You're right.. See my email just now in 4/9. I didn't understand when I read
this earlier, and I shouldn't have brought up the userspace side in this patch
review anyway.

>
> >
> >
> > The kernel call chain could have issues:
> > cxl_mem_identify/*() -> kernel caller allocates just enough space
> > cxl_mem_mbox_send_cmd() -> internal wrapper we created for v3
> > blows up in the spot you mention.
> >
> > The driver allocates enough space on the stack for all these calls, but yes, if
> > hardware is out of spec it would be problematic. In previous versions of this
> > series, there has been a check there. However, the ability to have hardware
> > return more data than expected is I believe the correct functionality here.
>
> It's absolutely fine to return more data, but we shouldn't copy it from the mailbox
> into memory that isn't big enough. We should be extremely paranoid about that.
>
>
>
> >
> > So my proposal is for now, since no real hardware exists, and the command set
> > here is so benign, we leave fixing this as a TODO.
> >
> > I can post a patch on top of this series to address this issue in a manner I
> > believe warrants discussing (kvzalloc max payload size buffers on open() and for
> > each driver instance).
>
> Or just sanity check the size against available buffer size before using it
> in mempcy_fromio.

I'll rework this...

>
> >
> > > > +
> > > > + memcpy_fromio(mbox_cmd->payload_out, payload, n);
> > > > + mbox_cmd->size_out = n;
> > > > + } else {
> > > > + mbox_cmd->size_out = 0;
> > > > + }
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > >
> > > ...
> > >
> > > > +
> > > > +/**
> > > > + * cxl_mem_mbox_send_cmd() - Send a mailbox command to a memory device.
> > > > + * @cxlm: The CXL memory device to communicate with.
> > > > + * @opcode: Opcode for the mailbox command.
> > > > + * @in: The input payload for the mailbox command.
> > > > + * @in_size: The length of the input payload
> > > > + * @out: Caller allocated buffer for the output.
> > > > + * @out_min_size: Minimum expected size of output.
> > > > + *
> > > > + * Context: Any context. Will acquire and release mbox_mutex.
> > > > + * Return:
> > > > + * * %>=0 - Number of bytes returned in @out.
> > > > + * * %-E2BIG - Payload is too large for hardware.
> > > > + * * %-EBUSY - Couldn't acquire exclusive mailbox access.
> > > > + * * %-EFAULT - Hardware error occurred.
> > > > + * * %-ENXIO - Command completed, but device reported an error.
> > > > + * * %-ENODATA - Not enough payload data returned by hardware.
> > > > + *
> > > > + * Mailbox commands may execute successfully yet the device itself reported an
> > > > + * error. While this distinction can be useful for commands from userspace, the
> > > > + * kernel will only be able to use results when both are successful.
> > > > + *
> > > > + * See __cxl_mem_mbox_send_cmd()
> > > > + */
> > > > +static int cxl_mem_mbox_send_cmd(struct cxl_mem *cxlm, u16 opcode, void *in,
> > > > + size_t in_size, void *out, size_t out_min_size)
> > > > +{
> > > > + struct mbox_cmd mbox_cmd = {
> > > > + .opcode = opcode,
> > > > + .payload_in = in,
> > > > + .size_in = in_size,
> > > > + .payload_out = out,
> > > > + };
> > > > + int rc;
> > > > +
> > > > + if (out_min_size > cxlm->payload_size)
> > > > + return -E2BIG;
> > > > +
> > > > + rc = cxl_mem_mbox_get(cxlm);
> > > > + if (rc)
> > > > + return rc;
> > > > +
> > > > + rc = __cxl_mem_mbox_send_cmd(cxlm, &mbox_cmd);
> > > > + cxl_mem_mbox_put(cxlm);
> > > > + if (rc)
> > > > + return rc;
> > > > +
> > > > + /* TODO: Map return code to proper kernel style errno */
> > > > + if (mbox_cmd.return_code != CXL_MBOX_SUCCESS)
> > > > + return -ENXIO;
> > > > +
> > > > + if (mbox_cmd.size_out < out_min_size)
> > > > + return -ENODATA;
> > > > +
> > > > + return mbox_cmd.size_out;
> > > > +}
> > > > +
> > > > +/**
> > > > + * cxl_mem_setup_regs() - Setup necessary MMIO.
> > > > + * @cxlm: The CXL memory device to communicate with.
> > > > + *
> > > > + * Return: 0 if all necessary registers mapped.
> > > > + *
> > > > + * A memory device is required by spec to implement a certain set of MMIO
> > > > + * regions. The purpose of this function is to enumerate and map those
> > > > + * registers.
> > > > + */
> > > > +static int cxl_mem_setup_regs(struct cxl_mem *cxlm)
> > > > +{
> > > > + struct device *dev = &cxlm->pdev->dev;
> > > > + int cap, cap_count;
> > > > + u64 cap_array;
> > > > +
> > > > + cap_array = readq(cxlm->regs + CXLDEV_CAP_ARRAY_OFFSET);
> > > > + if (FIELD_GET(CXLDEV_CAP_ARRAY_ID_MASK, cap_array) !=
> > > > + CXLDEV_CAP_ARRAY_CAP_ID)
> > > > + return -ENODEV;
> > > > +
> > > > + cap_count = FIELD_GET(CXLDEV_CAP_ARRAY_COUNT_MASK, cap_array);
> > > > +
> > > > + for (cap = 1; cap <= cap_count; cap++) {
> > > > + void __iomem *register_block;
> > > > + u32 offset;
> > > > + u16 cap_id;
> > > > +
> > > > + cap_id = readl(cxlm->regs + cap * 0x10) & 0xffff;
> > >
> > > Slight preference for FIELD_GET just for consistency.
> > >
> > > > + offset = readl(cxlm->regs + cap * 0x10 + 0x4);
> > > > + register_block = cxlm->regs + offset;
> > > > +
> > > > + switch (cap_id) {
> > > > + case CXLDEV_CAP_CAP_ID_DEVICE_STATUS:
> > > > + dev_dbg(dev, "found Status capability (0x%x)\n", offset);
> > > > + cxlm->status_regs = register_block;
> > > > + break;
> > > > + case CXLDEV_CAP_CAP_ID_PRIMARY_MAILBOX:
> > > > + dev_dbg(dev, "found Mailbox capability (0x%x)\n", offset);
> > > > + cxlm->mbox_regs = register_block;
> > > > + break;
> > > > + case CXLDEV_CAP_CAP_ID_SECONDARY_MAILBOX:
> > > > + dev_dbg(dev, "found Secondary Mailbox capability (0x%x)\n", offset);
> > > > + break;
> > > > + case CXLDEV_CAP_CAP_ID_MEMDEV:
> > > > + dev_dbg(dev, "found Memory Device capability (0x%x)\n", offset);
> > > > + cxlm->memdev_regs = register_block;
> > > > + break;
> > > > + default:
> > > > + dev_dbg(dev, "Unknown cap ID: %d (0x%x)\n", cap_id, offset);
> > > > + break;
> > > > + }
> > > > + }
> > > > +
> > > > + if (!cxlm->status_regs || !cxlm->mbox_regs || !cxlm->memdev_regs) {
> > > > + dev_err(dev, "registers not found: %s%s%s\n",
> > > > + !cxlm->status_regs ? "status " : "",
> > > > + !cxlm->mbox_regs ? "mbox " : "",
> > > > + !cxlm->memdev_regs ? "memdev" : "");
> > > > + return -ENXIO;
> > > > + }
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > >
> > > ...
> > >
> > > > +
> > > > +static struct cxl_mem *cxl_mem_create(struct pci_dev *pdev, u32 reg_lo,
> > > > + u32 reg_hi)
> > >
> > > I'm not really suggesting you change it at this point, but I'd have
> > > done the splitting of reg_lo up and the building of the offset at the call site
> > > rather than in here. I think that would have been slightly easier to follow.
> > >
> >
> > Noted. In future patches this is going to get reworked somewhat to support more
> > flexibility with register blocks.
> >
> > > > +{
> > > > + struct device *dev = &pdev->dev;
> > > > + struct cxl_mem *cxlm;
> > > > + void __iomem *regs;
> > > > + u64 offset;
> > > > + u8 bar;
> > > > + int rc;
> > > > +
> > > > + cxlm = devm_kzalloc(&pdev->dev, sizeof(*cxlm), GFP_KERNEL);
> > > > + if (!cxlm) {
> > > > + dev_err(dev, "No memory available\n");
> > > > + return NULL;
> > > > + }
> > > > +
> > > > + offset = ((u64)reg_hi << 32) | FIELD_GET(CXL_REGLOC_ADDR_MASK, reg_lo);
> > > > + bar = FIELD_GET(CXL_REGLOC_BIR_MASK, reg_lo);
> > > > +
> > > > + /* Basic sanity check that BAR is big enough */
> > > > + if (pci_resource_len(pdev, bar) < offset) {
> > > > + dev_err(dev, "BAR%d: %pr: too small (offset: %#llx)\n", bar,
> > > > + &pdev->resource[bar], (unsigned long long)offset);
> > > > + return NULL;
> > > > + }
> > > > +
> > > > + rc = pcim_iomap_regions(pdev, BIT(bar), pci_name(pdev));
> > > > + if (rc) {
> > > > + dev_err(dev, "failed to map registers\n");
> > > > + return NULL;
> > > > + }
> > > > + regs = pcim_iomap_table(pdev)[bar];
> > > > +
> > > > + mutex_init(&cxlm->mbox_mutex);
> > > > + cxlm->pdev = pdev;
> > > > + cxlm->regs = regs + offset;
> > > > +
> > > > + dev_dbg(dev, "Mapped CXL Memory Device resource\n");
> > > > + return cxlm;
> > > > +}
> > > >
> > > > static int cxl_mem_dvsec(struct pci_dev *pdev, int dvsec)
> > > > {
> > > > @@ -28,10 +479,65 @@ static int cxl_mem_dvsec(struct pci_dev *pdev, int dvsec)
> > > > return 0;
> > > > }
> > > >
> > > > +/**
> > > > + * cxl_mem_identify() - Send the IDENTIFY command to the device.
> > > > + * @cxlm: The device to identify.
> > > > + *
> > > > + * Return: 0 if identify was executed successfully.
> > > > + *
> > > > + * This will dispatch the identify command to the device and on success populate
> > > > + * structures to be exported to sysfs.
> > > > + */
> > > > +static int cxl_mem_identify(struct cxl_mem *cxlm)
> > > > +{
> > > > + struct cxl_mbox_identify {
> > > > + char fw_revision[0x10];
> > > > + __le64 total_capacity;
> > > > + __le64 volatile_capacity;
> > > > + __le64 persistent_capacity;
> > > > + __le64 partition_align;
> > > > + __le16 info_event_log_size;
> > > > + __le16 warning_event_log_size;
> > > > + __le16 failure_event_log_size;
> > > > + __le16 fatal_event_log_size;
> > > > + __le32 lsa_size;
> > > > + u8 poison_list_max_mer[3];
> > > > + __le16 inject_poison_limit;
> > > > + u8 poison_caps;
> > > > + u8 qos_telemetry_caps;
> > > > + } __packed id;
> > > > + int rc;
> > > > +
> > > > + rc = cxl_mem_mbox_send_cmd(cxlm, CXL_MBOX_OP_IDENTIFY, NULL, 0, &id,
> > > > + sizeof(id));
> > > > + if (rc < 0)
> > > > + return rc;
> > > > +
> > > > + /*
> > > > + * TODO: enumerate DPA map, as 'ram' and 'pmem' do not alias.
> > > > + * For now, only the capacity is exported in sysfs
> > > > + */
> > > > + cxlm->ram_range.start = 0;
> > > > + cxlm->ram_range.end = le64_to_cpu(id.volatile_capacity) - 1;
> > > > +
> > > > + cxlm->pmem_range.start = 0;
> > > > + cxlm->pmem_range.end = le64_to_cpu(id.persistent_capacity) - 1;
> > > > +
> > > > + memcpy(cxlm->firmware_version, id.fw_revision, sizeof(id.fw_revision));
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > static int cxl_mem_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> > > > {
> > > > struct device *dev = &pdev->dev;
> > > > - int regloc;
> > > > + struct cxl_mem *cxlm = NULL;
> > > > + int rc, regloc, i;
> > > > + u32 regloc_size;
> > > > +
> > > > + rc = pcim_enable_device(pdev);
> > > > + if (rc)
> > > > + return rc;
> > > >
> > > > regloc = cxl_mem_dvsec(pdev, PCI_DVSEC_ID_CXL_REGLOC_OFFSET);
> > > > if (!regloc) {
> > > > @@ -39,7 +545,40 @@ static int cxl_mem_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> > > > return -ENXIO;
> > > > }
> > > >
> > > > - return 0;
> > > > + /* Get the size of the Register Locator DVSEC */
> > > > + pci_read_config_dword(pdev, regloc + PCI_DVSEC_HEADER1, &regloc_size);
> > > > + regloc_size = FIELD_GET(PCI_DVSEC_HEADER1_LENGTH_MASK, regloc_size);
> > >
> > > The size field here is the dvsec length.. Let's say we only have one register block
> > > entry at +0x0c and +0x10
> > > From PCI spec :
> > >
> > > "DVSEC Length - This field indicates the number of bytes in the entire DVSEC structure, including the PCI
> > > Express Extended Capability Header, the DVSEC Header 1, DVSEC Header 2, and DVSEC vendor-specific
> > > registers."
> > >
> > > So here it would be 0x14
> > >
> > > > +
> > > > + regloc += PCI_DVSEC_ID_CXL_REGLOC_BLOCK1_OFFSET;
> > >
> > > We then shift regloc forward by +0xc
> > >
> > > > +
> > > > + for (i = regloc; i < regloc + regloc_size; i += 8) {
> > >
> > > This loop will then index form
> > > i= +0xc to i < +0c + 0x14 (0x20)
> > > i = 0xc, 0x14
> > >
> > > So that's indexing one more entry than is actually present.
> > > Should be something like
> > >
> > > for (i = regloc;
> > > i < regloc + regloc_size - PCI_DVSEC_ID_CXL_REGLOC_BLOCK1_OFFSET;
> > > i++)
> > >
> > > which will mean the only iteration for this example is the one with i == +0xC
> > >
> >
> > Good catch. I think this warrants rewriting a bit, let me know what you think?
> >
> > regloc += PCI_DVSEC_ID_CXL_REGLOC_BLOCK1_OFFSET;
> > regblocks = (regloc_size - PCI_DVSEC_ID_CXL_REGLOC_BLOCK1_OFFSET) / 8;
> >
> > for (i = 0; i < regblocks; i++, regloc+=8) {
> > pci_read_config_dword(pdev, regloc, &reg_lo);
> > pci_read_config_dword(pdev, regloc + 4, &reg_hi);
> >
> > ...
> > }
>
> That's fine.