On 21-02-12 13:27:06, Jonathan Cameron wrote: > On Thu, 11 Feb 2021 07:55:29 -0800 > Ben Widawsky <ben.widawsky@xxxxxxxxx> wrote: > > > On 21-02-11 09:55:48, Jonathan Cameron wrote: > > > On Wed, 10 Feb 2021 10:16:05 -0800 > > > Ben Widawsky <ben.widawsky@xxxxxxxxx> 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@xxxxxxxxxx> wrote: > > > > > > > > > > > > > On Tue, 9 Feb 2021 16:02:53 -0800 > > > > > > > Ben Widawsky <ben.widawsky@xxxxxxxxx> 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@xxxxxxxxx> > > > > > > > > Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx> > > > > > > > > > > > > > > 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 > > > > Some background because I forget what I've said previously... It's unfortunate > > that the spec maxes at 1M mailbox size but has enough bits in the length field > > to support 2M-1. I've made some requests to have this fixed, so maybe 3.0 won't > > be awkward like this. > > Agreed spec should be tighter here, but I'd argue over 1M indicates buggy hardware. > > > > > I think it makes sense to do as you suggested. One question though, do you have > > an opinion on we return to the caller as the output payload size, do we cap it > > at 1M also, or are we honest? > > > > - if (out_len && mbox_cmd->payload_out) > > - memcpy_fromio(mbox_cmd->payload_out, payload, out_len); > > + if (out_len && mbox_cmd->payload_out) { > > + size_t n = min_t(size_t, cxlm->payload_size, out_len); > > + memcpy_fromio(mbox_cmd->payload_out, payload, n); > > + } > > Ah, I read emails in wrong order. What you have is what I expected and got > confused about in your other email. > > > > > So... > > mbox_cmd->size_out = out_len; > > mbox_cmd->size_out = n; > > Good question. My gut says the second one. > Maybe it's worth a warning print to let us know something > unexpected happened. > I also prefer 'n', It's unfortunate though if userspace hits this condition, it would have to scrape kernel logs to find out. Perhaps though userspace wouldn't ever really care. > > > > > > > > > > > > > > > > > > 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] > > > > > > > >
