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Date:   Fri, 8 Apr 2022 11:52:49 -0400
From:   Aristeu Rozanski <aris@redhat.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc:     linux-kernel@vger.kernel.org, Ard Biesheuvel <ardb@kernel.org>,
        Will Deacon <will@kernel.org>,
        Hanjun Guo <guohanjun@huawei.com>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Veronika kabatova <vkabatov@redhat.com>,
        Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH] ACPI: osl: Fix BERT error region memory mapping
Message-ID: <20220408155249.mdkmdttykmoenqeu@redhat.com>
References: <20220407105120.1280-1-lorenzo.pieralisi@arm.com>
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On Thu, Apr 07, 2022 at 11:51:20AM +0100, Lorenzo Pieralisi 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@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@arm.com>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Hanjun Guo <guohanjun@huawei.com>
> Cc: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.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)

I've tested this patch with the reproducer and I was unable to reproduce
the issue.

Tested-by: Aristeu Rozanski <aris@redhat.com>

-- 
Aristeu