From: Ben Widawsky <ben.widawsky@intel.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-cxl@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux PCI <linux-pci@vger.kernel.org>,
Linux ACPI <linux-acpi@vger.kernel.org>,
Ira Weiny <ira.weiny@intel.com>,
Vishal Verma <vishal.l.verma@intel.com>,
"Kelley, Sean V" <sean.v.kelley@intel.com>,
Rafael Wysocki <rafael.j.wysocki@intel.com>,
Bjorn Helgaas <helgaas@kernel.org>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>,
Jon Masters <jcm@jonmasters.org>,
Chris Browy <cbrowy@avery-design.com>,
Randy Dunlap <rdunlap@infradead.org>,
Christoph Hellwig <hch@infradead.org>
Subject: Re: [RFC PATCH 11/14] cxl/mem: Add a "RAW" send command
Date: Wed, 16 Dec 2020 12:42:05 -0800 [thread overview]
Message-ID: <20201216204205.acum2sf652aspah3@intel.com> (raw)
In-Reply-To: <CAPcyv4hRJRP+55QHxQYsAoE7V601+YMWgtEvzLimKRO8b4Jrjg@mail.gmail.com>
On 20-12-09 14:38:49, Dan Williams wrote:
> On Tue, Dec 8, 2020 at 4:24 PM Ben Widawsky <ben.widawsky@intel.com> wrote:
> >
> > The CXL memory device send interface will have a number of supported
> > commands. The raw command is not such a command. Raw commands allow
> > userspace to send a specified opcode to the underlying hardware and
> > bypass all driver checks on the command. This is useful for a couple of
> > usecases, mainly:
> > 1. Undocumented vendor specific hardware commands
> > 2. Prototyping new hardware commands not yet supported by the driver
> >
> > While this all sounds very powerful it comes with a couple of caveats:
> > 1. Bug reports using raw commands will not get the same level of
> > attention as bug reports using supported commands (via taint).
> > 2. Supported commands will be rejected by the RAW command.
> >
> > Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> > ---
> > drivers/cxl/mem.c | 32 ++++++++++++++++++++++++++++++++
> > include/uapi/linux/cxl_mem.h | 14 ++++++++++++--
> > 2 files changed, 44 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> > index 0bf03afc0c80..a2cea7ac7cc6 100644
> > --- a/drivers/cxl/mem.c
> > +++ b/drivers/cxl/mem.c
> > @@ -115,6 +115,7 @@ struct cxl_mem_command {
> >
> > static struct cxl_mem_command mem_commands[] = {
> > CXL_CMD(INVALID, NONE, 0, 0, "Reserved", false, 0),
> > + CXL_CMD(RAW, TAINT, ~0, ~0, "Raw", true, 0),
>
> Why is the taint indication in the ABI? It seems like it only needs to
> be documented.
>
It's removed per the previous patch discussion.
> > };
> >
> > static int cxl_mem_wait_for_doorbell(struct cxl_mem *cxlm)
> > @@ -326,6 +327,20 @@ static int cxl_mem_count_commands(void)
> > return n;
> > };
> >
> > +static struct cxl_mem_command *cxl_mem_find_command(u16 opcode)
> > +{
> > + int i;
> > +
> > + for (i = 0; i < ARRAY_SIZE(mem_commands); i++) {
> > + struct cxl_mem_command *c = &mem_commands[i];
> > +
> > + if (c->opcode == opcode)
> > + return c;
> > + }
> > +
> > + return NULL;
> > +};
> > +
> > /**
> > * handle_mailbox_cmd_from_user() - Dispatch a mailbox command.
> > * @cxlmd: The CXL memory device to communicate with.
> > @@ -421,6 +436,23 @@ static int cxl_validate_cmd_from_user(struct cxl_send_command __user *user_cmd,
> > c = &mem_commands[cmd.id];
> > info = &c->info;
> >
> > + /* Checks are bypassed for raw commands but along comes the taint! */
> > + if (cmd.id == CXL_MEM_COMMAND_ID_RAW) {
> > + struct cxl_mem_command temp =
> > + CXL_CMD(RAW, NONE, cmd.size_in, cmd.size_out, "Raw",
> > + true, cmd.raw.opcode);
>
> Oh, I thought CXL_CMD() was only used to populate the mem_commands
> array. Feels out of place to use it here when all it is doing is
> updating the size_{in,out} and opcode fields. Mainly I'm interested in
> CXL_CMD() enforcing that the command-id is the mem_commands index.
>
Agreed and removed.
> > +
> > + if (cmd.raw.rsvd)
> > + return -EINVAL;
> > +
> > + if (cxl_mem_find_command(cmd.raw.opcode))
> > + return -EPERM;
> > +
> > + add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
>
> TAINT_WARN seems the wrong value, especially since no WARN has
> occurred. I feel that this is more in the spirit of
> TAINT_PROPRIETARY_MODULE, TAINT_OVERRIDDEN_ACPI_TABLE, and
> TAINT_OOT_MODULE. How about a new TAINT_RAW_PASSTHROUGH? I could use
> this for the acpi/nfit driver as well to disclaim responsibility for
> system errors that can result from not using the nominal
> kernel-provided commands.
I like it.
next prev parent reply other threads:[~2020-12-16 20:42 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-09 0:24 [RFC PATCH v2 00/14] CXL 2.0 Support Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH v2 01/14] docs: cxl: Add basic documentation Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH v2 02/14] cxl/acpi: Add an acpi_cxl module for the CXL interconnect Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH v2 03/14] cxl/acpi: add OSC support Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH v2 04/14] cxl/mem: Introduce a driver for CXL-2.0-Type-3 endpoints Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH v2 05/14] cxl/mem: Map memory device registers Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH v2 06/14] cxl/mem: Find device capabilities Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH v2 07/14] cxl/mem: Implement polled mode mailbox Ben Widawsky
2021-01-07 19:05 ` Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH v2 08/14] cxl/mem: Register CXL memX devices Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH 09/14] cxl/mem: Add basic IOCTL interface Ben Widawsky
2020-12-09 1:37 ` Dan Williams
2020-12-09 2:12 ` Ben Widawsky
2020-12-09 3:33 ` Dan Williams
2020-12-09 16:23 ` Ben Widawsky
2020-12-10 3:32 ` Randy Dunlap
2020-12-14 17:29 ` Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH 10/14] cxl/mem: Add send command Ben Widawsky
2020-12-09 22:06 ` Dan Williams
2020-12-15 21:43 ` Ben Widawsky
2020-12-15 22:03 ` Dan Williams
2020-12-15 22:17 ` Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH 11/14] cxl/mem: Add a "RAW" " Ben Widawsky
2020-12-09 22:38 ` Dan Williams
2020-12-16 20:42 ` Ben Widawsky [this message]
2020-12-09 0:24 ` [RFC PATCH 12/14] cxl: Add basic debugging Ben Widawsky
2020-12-09 1:17 ` Dan Williams
2020-12-09 2:04 ` Ben Widawsky
2020-12-09 3:06 ` Dan Williams
2020-12-16 21:02 ` Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH 13/14] MAINTAINERS: Add maintainers of the CXL driver Ben Widawsky
2020-12-09 0:24 ` [RFC PATCH 14/14] WIP/cxl/mem: Add get firmware for testing Ben Widawsky
2020-12-10 0:42 ` Dan Williams
2020-12-09 0:33 ` [RFC PATCH v2 00/14] CXL 2.0 Support Verma, Vishal L
2020-12-09 0:47 ` Ben Widawsky
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