Re: [Xen-devel] [PATCH 2/6] x86/boot: Map the trampoline as read-only

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.01.2020 16:54, Andrew Cooper wrote:
> c/s ec92fcd1d08, which caused the trampoline GDT Access bits to be set,
> removed the final writes which occurred between enabling paging and switching
> to the high mappings.  There don't plausibly need to be any memory writes in
> few instructions is takes to perform this transition.
> 
> As a consequence, we can remove the RWX mapping of the trampoline.  It is RX
> via its identity mapping below 1M, and RW via the directmap.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

> This probably wants backporting, alongside ec92fcd1d08 if it hasn't yet.

This is just cleanup, largely cosmetic in nature. It could be argued
that once the directmap has disappeared this can serve as additional
proof that the trampoline range has no (intended) writable mappings
anymore, but prior to that point I don't see much further benefit.
Could you expand on the reasons why you see both as backporting
candidates?


Jan

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