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Re: [PATCH V3 (resend) 06/19] x86: Add a boot option to enable and disable the direct map
- To: Elias El Yandouzi <eliasely@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 15 May 2024 18:02:24 +0200
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- Cc: julien@xxxxxxx, pdurrant@xxxxxxxxxx, dwmw@xxxxxxxxxx, Hongyan Xia <hongyxia@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 15 May 2024 16:02:35 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 13.05.2024 15:40, Elias El Yandouzi wrote:
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -799,6 +799,18 @@ that enabling this option cannot guarantee anything
> beyond what underlying
> hardware guarantees (with, where available and known to Xen, respective
> tweaks applied).
>
> +### directmap (x86)
> +> `= <boolean>`
> +
> +> Default: `true`
> +
> +Enable or disable the directmap region in Xen.
> +
> +By default, Xen creates the directmap region which maps physical memory
> +in that region. Setting this to no will sparsely populate the directmap,
> +blocking exploits that leak secrets via speculative memory access in the
> +directmap.
Along the lines of remarks on comments and descriptions: I think we ought to
reserve "directmap=no" to a future where there really is the option of not
having anything direct-mapped. Right now imo that option form ought to be
invalid, and only "directmap=sparse" should be recognized (alongside
"directmap=yes" of course).
Jan
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