linux-kernel - Re: [PATCH] iommu/vt-d: Check VT-d RMRR region in BIOS is reported as reserved

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Message-ID: <20191016075120.GB32232@8bytes.org>
Date:   Wed, 16 Oct 2019 09:51:21 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Yian Chen <yian.chen@...el.com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, David Woodhouse <dwmw2@...radead.org>,
        Ashok Raj <ashok.raj@...el.com>,
        Sohil Mehta <sohil.mehta@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH] iommu/vt-d: Check VT-d RMRR region in BIOS is reported
 as reserved

Hi,

On Tue, Oct 15, 2019 at 09:49:32AM -0700, Yian Chen wrote:
> VT-d RMRR (Reserved Memory Region Reporting) regions are reserved
> for device use only and should not be part of allocable memory pool of OS.
> 
> BIOS e820_table reports complete memory map to OS, including OS usable
> memory ranges and BIOS reserved memory ranges etc.
> 
> x86 BIOS may not be trusted to include RMRR regions as reserved type
> of memory in its e820 memory map, hence validate every RMRR entry
> with the e820 memory map to make sure the RMRR regions will not be
> used by OS for any other purposes.

Are there real systems in the wild where this is a problem?

> +static inline int __init
> +arch_rmrr_sanity_check(struct acpi_dmar_reserved_memory *rmrr)
> +{
> +	u64 start = rmrr->base_address;
> +	u64 end = rmrr->end_address + 1;
> +
> +	if (e820__mapped_all(start, end, E820_TYPE_RESERVED))
> +		return 0;
> +
> +	pr_err(FW_BUG "No firmware reserved region can cover this RMRR [%#018Lx-%#018Lx], contact BIOS vendor for fixes\n",
> +	       start, end - 1);
> +	return -EFAULT;
> +}

Why -EFAULT, there is no fault involved? Usibg -EINVAL seems to be a better choice.