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Re: [PATCH v4 01/11] x86/HVM: improve CET-IBT pruning of ENDBR
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 5 Mar 2025 14:47:58 +0000
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 05 Mar 2025 14:48:10 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 25/02/2025 11:37 am, Jan Beulich wrote:
> __init{const,data}_cf_clobber can have an effect only for pointers
> actually populated in the respective tables. While not the case for SVM
> right now, VMX installs a number of pointers only under certain
> conditions. Hence the respective functions would have their ENDBR purged
> only when those conditions are met. Invoke "pruning" functions after
> having copied the respective tables, for them to install any "missing"
> pointers.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
I don't especially like this, but I can't suggest anything better right
now, so
Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> This is largely cosmetic for present hardware, which when supporting
> CET-IBT likely also supports all of the advanced VMX features for which
> hook pointers are installed conditionally. The only case this would make
> a difference there is when use of respective features was suppressed via
> command line option (where available). For future hooks it may end up
> relevant even by default, and it also would be if AMD started supporting
> CET-IBT; right now it matters only for .pi_update_irte, as iommu_intpost
> continues to default to off.
This is all mixed up in the breakage underpinning nested-virt (the false
believe that there is some kind of "global" idea of how a VMCS is
configured).
I suspect this might just disappear in due course.
> Originally I had meant to put the SVM and VMX functions in presmp-
> initcalls, but hvm/{svm,vmx}/built_in.o are linked into hvm/built_in.o
> before hvm/hvm.o. And I don't think I want to fiddle with link order
> here.
Why does the link order matter?
~Andrew
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