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Re: [PATCH 4/4] iommu/x86: make unity range checking more strict
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 6 Feb 2024 12:49:08 +0100
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- Cc: Paul Durrant <paul@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 06 Feb 2024 11:49:14 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 01.02.2024 18:01, Roger Pau Monne wrote:
> Currently when a unity range overlaps with memory being used as RAM by the
> hypervisor the result would be that the IOMMU gets disabled. However that's
> not enough, as even with the IOMMU disabled the device will still access the
> affected RAM areas.
Hmm, no, I think this is going too far. Not the least because it is
s/will/may/. But also because if we really wanted such behavior, we
ought to also parse the respective ACPI tables when the "iommu=off".
> Note that IVMD or RMRR ranges being placed over RAM is a firmware bug.
As written this is wrong: They're typically in RAM, just that the E820
type for that range should not be RAM_TYPE_CONVENTIONAL.
> Doing so also allows to simplify the code and use a switch over the reported
> memory type(s).
I'm afraid this isn't right either: page_get_ram_type() can set
multiple bits in its output.
Jan
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