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Re: [RFC PATCH v1 10/15] KVM: VMX: Use WRMSRNS or its immediate form when available
- To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
- From: Borislav Petkov <bp@xxxxxxxxx>
- Date: Mon, 31 Mar 2025 22:38:11 +0200
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- Cc: "Xin Li (Intel)" <xin@xxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-perf-users@xxxxxxxxxxxxxxx, linux-hyperv@xxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxxx, linux-edac@xxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-ide@xxxxxxxxxxxxxxx, linux-pm@xxxxxxxxxxxxxxx, bpf@xxxxxxxxxxxxxxx, llvm@xxxxxxxxxxxxxxx, tglx@xxxxxxxxxxxxx, mingo@xxxxxxxxxx, dave.hansen@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, hpa@xxxxxxxxx, jgross@xxxxxxxx, andrew.cooper3@xxxxxxxxxx, peterz@xxxxxxxxxxxxx, acme@xxxxxxxxxx, namhyung@xxxxxxxxxx, mark.rutland@xxxxxxx, alexander.shishkin@xxxxxxxxxxxxxxx, jolsa@xxxxxxxxxx, irogers@xxxxxxxxxx, adrian.hunter@xxxxxxxxx, kan.liang@xxxxxxxxxxxxxxx, wei.liu@xxxxxxxxxx, ajay.kaher@xxxxxxxxxxxx, alexey.amakhalov@xxxxxxxxxxxx, bcm-kernel-feedback-list@xxxxxxxxxxxx, tony.luck@xxxxxxxxx, pbonzini@xxxxxxxxxx, vkuznets@xxxxxxxxxx, seanjc@xxxxxxxxxx, luto@xxxxxxxxxx, boris.ostrovsky@xxxxxxxxxx, kys@xxxxxxxxxxxxx, haiyangz@xxxxxxxxxxxxx, decui@xxxxxxxxxxxxx
- Delivery-date: Mon, 31 Mar 2025 20:39:14 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Mon, Mar 31, 2025 at 04:27:23PM -0400, Konrad Rzeszutek Wilk wrote:
> Is that the right path forward?
>
> That is replace the MSR write to disable speculative execution with a
> non-serialized WRMSR? Doesn't that mean the WRMSRNS is speculative?
Ha, interesting question.
If the WRMSR is non-serializing, when do speculative things like indirect
branches and the like get *actually* cleared and can such a speculation window
be used to leak branch data even if IBRS is actually enabled for example...
Fun.
This change needs to be run by hw folks and I guess until then WRMSRNS should
not get anywhere near mitigation MSRs like SPEC_CTRL or PRED_CMD...
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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