Re: [PATCH] ACPI: osl: Fix BERT error region memory mapping

[Rafael J. Wysocki]

On Wed, Apr 13, 2022 at 7:41 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Thu, 7 Apr 2022 at 12:51, Lorenzo Pieralisi
> <lorenzo.pieralisi@xxxxxxx> wrote:
> >
> > Currently the sysfs interface maps the BERT error region as "memory"
> > (through acpi_os_map_memory()) in order to copy the error records into
> > memory buffers through memory operations (eg memory_read_from_buffer()).
> >
> > The OS system cannot detect whether the BERT error region is part of
> > system RAM or it is "device memory" (eg BMC memory) and therefore it
> > cannot detect which memory attributes the bus to memory support (and
> > corresponding kernel mapping, unless firmware provides the required
> > information).
> >
> > The acpi_os_map_memory() arch backend implementation determines the
> > mapping attributes. On arm64, if the BERT error region is not present in
> > the EFI memory map, the error region is mapped as device-nGnRnE; this
> > triggers alignment faults since memcpy unaligned accesses are not
> > allowed in device-nGnRnE regions.
> >
> > The ACPI sysfs code cannot therefore map by default the BERT error
> > region with memory semantics but should use a safer default.
> >
> > Change the sysfs code to map the BERT error region as MMIO (through
> > acpi_os_map_iomem()) and use the memcpy_fromio() interface to read the
> > error region into the kernel buffer.
> >
> > Link: https://lore.kernel.org/linux-arm-kernel/31ffe8fc-f5ee-2858-26c5-0fd8bdd68702@xxxxxxx
> > Link: https://lore.kernel.org/linux-acpi/CAJZ5v0g+OVbhuUUDrLUCfX_mVqY_e8ubgLTU98=jfjTeb4t+Pw@xxxxxxxxxxxxxx
> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> > Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> > Cc: Will Deacon <will@xxxxxxxxxx>
> > Cc: Hanjun Guo <guohanjun@xxxxxxxxxx>
> > Cc: Sudeep Holla <sudeep.holla@xxxxxxx>
> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
>
> Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>

Applied as 5.19 material, thanks!

> > ---
> >  drivers/acpi/sysfs.c | 25 ++++++++++++++++++-------
> >  1 file changed, 18 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
> > index a4b638bea6f1..cc2fe0618178 100644
> > --- a/drivers/acpi/sysfs.c
> > +++ b/drivers/acpi/sysfs.c
> > @@ -415,19 +415,30 @@ static ssize_t acpi_data_show(struct file *filp, struct kobject *kobj,
> >                               loff_t offset, size_t count)
> >  {
> >         struct acpi_data_attr *data_attr;
> > -       void *base;
> > -       ssize_t rc;
> > +       void __iomem *base;
> > +       ssize_t size;
> >
> >         data_attr = container_of(bin_attr, struct acpi_data_attr, attr);
> > +       size = data_attr->attr.size;
> > +
> > +       if (offset < 0)
> > +               return -EINVAL;
> > +
> > +       if (offset >= size)
> > +               return 0;
> >
> > -       base = acpi_os_map_memory(data_attr->addr, data_attr->attr.size);
> > +       if (count > size - offset)
> > +               count = size - offset;
> > +
> > +       base = acpi_os_map_iomem(data_attr->addr, size);
> >         if (!base)
> >                 return -ENOMEM;
> > -       rc = memory_read_from_buffer(buf, count, &offset, base,
> > -                                    data_attr->attr.size);
> > -       acpi_os_unmap_memory(base, data_attr->attr.size);
> >
> > -       return rc;
> > +       memcpy_fromio(buf, base + offset, count);
> > +
> > +       acpi_os_unmap_iomem(base, size);
> > +
> > +       return count;
> >  }
> >
> >  static int acpi_bert_data_init(void *th, struct acpi_data_attr *data_attr)
> > --
> > 2.31.0
> >