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

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Message-ID: <CA+tGwnmjv0nj11zRtcu8ZLCng9d94E1rVn71dfopHK16WiuMUQ@mail.gmail.com>
Date:   Fri, 8 Apr 2022 15:54:17 +0200
From:   Veronika Kabatova <vkabatov@...hat.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Will Deacon <will@...nel.org>,
        Hanjun Guo <guohanjun@...wei.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Robin Murphy <robin.murphy@....com>,
        Aristeu Rozanski <aris@...hat.com>
Subject: Re: [PATCH] ACPI: osl: Fix BERT error region memory mapping

On Thu, Apr 7, 2022 at 12:51 PM Lorenzo Pieralisi
<lorenzo.pieralisi@....com> 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.
>

Hi,

I tested this patch on top of the arm tree for-kernelci branch (a2c0b0fbe014).
I wasn't able to trigger the original problem on the same HW, and the patch
didn't introduce any new issues on these runs, nor on other randomly
chosen aarch64 machines.

Tested-by: Veronika Kabatova <vkabatov@...hat.com>


> Link: https://lore.kernel.org/linux-arm-kernel/31ffe8fc-f5ee-2858-26c5-0fd8bdd68702@arm.com
> Link: https://lore.kernel.org/linux-acpi/CAJZ5v0g+OVbhuUUDrLUCfX_mVqY_e8ubgLTU98=jfjTeb4t+Pw@mail.gmail.com
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Cc: Ard Biesheuvel <ardb@...nel.org>
> Cc: Will Deacon <will@...nel.org>
> Cc: Hanjun Guo <guohanjun@...wei.com>
> Cc: Sudeep Holla <sudeep.holla@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> ---
>  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
>