Re: [PATCH v2 2/8] cxl/mem: Find device capabilities

Ben Widawsky
2021-02-11T18:27:48Z

On 21-02-11 09:55:48, Jonathan Cameron wrote:
> On Wed, 10 Feb 2021 10:16:05 -0800
> Ben Widawsky <ben.widawsky@intel.com> wrote:
>
> > On 21-02-10 08:55:57, Ben Widawsky wrote:
> > > On 21-02-10 15:07:59, Jonathan Cameron wrote:
> > > > On Wed, 10 Feb 2021 13:32:52 +0000
> > > > Jonathan Cameron <Jonathan.Cameron@Huawei.com> wrote:
> > > >
> > > > > On Tue, 9 Feb 2021 16:02:53 -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>
> > > > >
> > > > > Hi Ben,
> > > > >
> > > > >
> > > > > > +/**
> > > > > > + * cxl_mem_mbox_send_cmd() - Send a mailbox command to a memory device.
> > > > > > + * @cxlm: The CXL memory device to communicate with.
> > > > > > + * @mbox_cmd: Command to send to the memory device.
> > > > > > + *
> > > > > > + * Context: Any context. Expects mbox_lock 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.
> > > > >
> > > > > cxl_xfer_log() doesn't check mbox_cmd->return_code and for my test it currently
> > > > > enters an infinite loop as a result.
> > >
> > > I meant to fix that.
> > >
> > > > >
> > > > > I haven't checked other paths, but to my mind it is not a good idea to require
> > > > > two levels of error checking - the example here proves how easy it is to forget
> > > > > one.
> > >
> > > Demonstrably, you're correct. I think it would be good to have a kernel only
> > > mbox command that does the error checking though. Let me type something up and
> > > see how it looks.
> >
> > Hi Jonathan. What do you think of this? The bit I'm on the fence about is if I
> > should validate output size too. I like the simplicity as it is, but it requires
> > every caller to possibly check output size, which is kind of the same problem
> > you're originally pointing out.
>
> The simplicity is good and this is pretty much what I expected you would end up with
> (always reassuring)
>
> For the output, perhaps just add another parameter to the wrapper for minimum
> output length expected?
>
> Now you mention the length question. It does rather feel like there should also
> be some protection on memcpy_fromio() copying too much data if the hardware
> happens to return an unexpectedly long length. Should never happen, but
> the hardening is worth adding anyway given it's easy to do.
>
> Jonathan
>

I like it.

diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index 2e199b05f686..58071a203212 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -293,7 +293,7 @@ static void cxl_mem_mbox_put(struct cxl_mem *cxlm)
* See __cxl_mem_mbox_send_cmd()
*/
static int cxl_mem_mbox_send_cmd(struct cxl_mem *cxlm, u16 opcode, u8 *in,
- size_t in_size, u8 *out)
+ size_t in_size, u8 *out, size_t out_min_size)
{
struct mbox_cmd mbox_cmd = {
.opcode = opcode,
@@ -303,6 +303,9 @@ static int cxl_mem_mbox_send_cmd(struct cxl_mem *cxlm, u16 opcode, u8 *in,
};
int rc;

+ if (out_min_size > cxlm->payload_size)
+ return -E2BIG;
+
rc = cxl_mem_mbox_get(cxlm);
if (rc)
return rc;
@@ -316,6 +319,9 @@ static int cxl_mem_mbox_send_cmd(struct cxl_mem *cxlm, u16 opcode, u8 *in,
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;
}

@@ -505,15 +511,10 @@ static int cxl_mem_identify(struct cxl_mem *cxlm)
int rc;

rc = cxl_mem_mbox_send_cmd(cxlm, CXL_MBOX_OP_IDENTIFY, NULL, 0,
- (u8 *)&id);
+ (u8 *)&id, sizeof(id));
if (rc < 0)
return rc;

- if (rc < sizeof(id)) {
- dev_err(&cxlm->pdev->dev, "Short identify data\n");
- return -ENXIO;
- }
-
/*
* TODO: enumerate DPA map, as 'ram' and 'pmem' do not alias.
* For now, only the capacity is exported in sysfs

>
> >
> > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> > index 55c5f5a6023f..ad7b2077ab28 100644
> > --- a/drivers/cxl/mem.c
> > +++ b/drivers/cxl/mem.c
> > @@ -284,7 +284,7 @@ static void cxl_mem_mbox_timeout(struct cxl_mem *cxlm,
> > }
> >
> > /**
> > - * cxl_mem_mbox_send_cmd() - Send a mailbox command to a memory device.
> > + * __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.
> > *
> > @@ -296,7 +296,8 @@ static void cxl_mem_mbox_timeout(struct cxl_mem *cxlm,
> > * This is a generic form of the CXL mailbox send command, thus the only I/O
> > * operations used are cxl_read_mbox_reg(). Memory devices, and perhaps other
> > * types of CXL devices may have further information available upon error
> > - * conditions.
> > + * 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
> > @@ -304,8 +305,8 @@ static void cxl_mem_mbox_timeout(struct cxl_mem *cxlm,
> > * 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)
> > +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;
> > @@ -469,6 +470,54 @@ static void cxl_mem_mbox_put(struct cxl_mem *cxlm)
> > mutex_unlock(&cxlm->mbox_mutex);
> > }
> >
> > +/**
> > + * 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.
> > + *
> > + * Context: Any context. Will acquire and release mbox_mutex.
> > + * Return:
> > + * * %>=0 - Number of bytes returned in @out.
> > + * * %-EBUSY - Couldn't acquire exclusive mailbox access.
> > + * * %-EFAULT - Hardware error occurred.
> > + * * %-ENXIO - Command completed, but device reported an error.
> > + *
> > + * 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 often only care when both are successful.
> > + *
> > + * See __cxl_mem_mbox_send_cmd()
> > + */
> > +static int cxl_mem_mbox_send_cmd(struct cxl_mem *cxlm, u16 opcode, u8 *in,
> > + size_t in_size, u8 *out)
> > +{
> > + struct mbox_cmd mbox_cmd = {
> > + .opcode = opcode,
> > + .payload_in = in,
> > + .size_in = in_size,
> > + .payload_out = out,
> > + };
> > + int rc;
> > +
> > + 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;
> > +
> > + return mbox_cmd.size_out;
> > +}
> > +
> > /**
> > * handle_mailbox_cmd_from_user() - Dispatch a mailbox command.
> > * @cxlmd: The CXL memory device to communicate with.
> > @@ -1380,33 +1429,18 @@ static int cxl_mem_identify(struct cxl_mem *cxlm)
> > u8 poison_caps;
> > u8 qos_telemetry_caps;
> > } __packed id;
> > - struct mbox_cmd mbox_cmd = {
> > - .opcode = CXL_MBOX_OP_IDENTIFY,
> > - .payload_out = &id,
> > - .size_in = 0,
> > - };
> > int rc;
> >
> > - /* Retrieve initial device memory map */
> > - 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)
> > + rc = cxl_mem_mbox_send_cmd(cxlm, CXL_MBOX_OP_IDENTIFY, NULL, 0,
> > + (u8 *)&id);
> > + if (rc < 0)
> > return rc;
> >
> > - /* TODO: Handle retry or reset responses from firmware. */
> > - if (mbox_cmd.return_code != CXL_MBOX_SUCCESS) {
> > - dev_err(&cxlm->pdev->dev, "Mailbox command failed (%d)\n",
> > - mbox_cmd.return_code);
> > + if (rc < sizeof(id)) {
> > + dev_err(&cxlm->pdev->dev, "Short identify data\n",
> > return -ENXIO;
> > }
> >
> > - if (mbox_cmd.size_out != sizeof(id))
> > - return -ENXIO;
> > -
> > /*
> > * TODO: enumerate DPA map, as 'ram' and 'pmem' do not alias.
> > * For now, only the capacity is exported in sysfs
> >
> >
> > [snip]