linux-kernel - Re: [PATCH v1] ACPI: sysfs: Enable ACPI sysfs support for CCEL records

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Message-ID: <CAJZ5v0jpJ1yq7bS7TLLAzCL6k-_HWCVSQLx4U=3wuM_2=V-sHQ@mail.gmail.com>
Date:   Mon, 20 Mar 2023 18:35:10 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Rafael J Wysocki <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] ACPI: sysfs: Enable ACPI sysfs support for CCEL records

On Mon, Mar 20, 2023 at 6:34 PM Sathyanarayanan Kuppuswamy
<sathyanarayanan.kuppuswamy@...ux.intel.com> wrote:
>
> Hi Rafael,
>
> On 3/20/23 10:15 AM, Rafael J. Wysocki wrote:
> > On Thu, Mar 2, 2023 at 8:13 AM Kuppuswamy Sathyanarayanan
> > <sathyanarayanan.kuppuswamy@...ux.intel.com> wrote:
> >>
> >> The Confidential Computing Event Log (CCEL) table provides the address
> >> and length of the CCEL records area in UEFI reserved memory. To access
> >> these records, userspace can use /dev/mem to retrieve them. But
> >> '/dev/mem' is not enabled on many systems for security reasons.
> >>
> >> So to allow user space access these event log records without the
> >> /dev/mem interface, add support to access it via sysfs interface. The
> >> ACPI driver has provided read only access to BERT records area via
> >> '/sys/firmware/acpi/tables/data/BERT' in sysfs. So follow the same way,
> >> and add support for /sys/firmware/acpi/tables/data/CCEL to enable
> >> read-only access to the CCEL recorids area.
> >>
> >> More details about the CCEL table can be found in ACPI specification
> >> r6.5, sec titled "CC Event Log ACPI Table".
> >>
> >> Original-patch-by: Haibo Xu <haibo1.xu@...el.com>
> >> [Original patch is for TDEL table, modified it for CCEL support]
> >> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> >> ---
> >>  drivers/acpi/sysfs.c | 17 +++++++++++++++++
> >>  1 file changed, 17 insertions(+)
> >>
> >> diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
> >> index 7db3b530279b..afeac925b31b 100644
> >> --- a/drivers/acpi/sysfs.c
> >> +++ b/drivers/acpi/sysfs.c
> >> @@ -458,11 +458,28 @@ static int acpi_bert_data_init(void *th, struct acpi_data_attr *data_attr)
> >>         return sysfs_create_bin_file(tables_data_kobj, &data_attr->attr);
> >>  }
> >>
> >> +static int acpi_ccel_data_init(void *th, struct acpi_data_attr *data_attr)
> >> +{
> >> +       struct acpi_table_ccel *ccel = th;
> >> +
> >> +       if (ccel->header.length < sizeof(struct acpi_table_ccel) ||
> >> +           !(ccel->log_area_start_address) || !(ccel->log_area_minimum_length)) {
> >
> > The inner parens in this line are not necessary AFAICS.
> >
> > Otherwise I have no objections.
>
> Yes. We can do without it. Shall I submit v2 with this change, or you want to
> fix it when applying?

I would appreciate a v2.

> >
> >> +               kfree(data_attr);
> >> +               return -EINVAL;
> >> +       }
> >> +       data_attr->addr = ccel->log_area_start_address;
> >> +       data_attr->attr.size = ccel->log_area_minimum_length;
> >> +       data_attr->attr.attr.name = "CCEL";
> >> +
> >> +       return sysfs_create_bin_file(tables_data_kobj, &data_attr->attr);
> >> +}
> >> +
> >>  static struct acpi_data_obj {
> >>         char *name;
> >>         int (*fn)(void *, struct acpi_data_attr *);
> >>  } acpi_data_objs[] = {
> >>         { ACPI_SIG_BERT, acpi_bert_data_init },
> >> +       { ACPI_SIG_CCEL, acpi_ccel_data_init },
> >>  };
> >>
> >>  #define NUM_ACPI_DATA_OBJS ARRAY_SIZE(acpi_data_objs)
> >> --
>
> --