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

[Ard Biesheuvel]

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>

> ---
>  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
>