linux-kernel - Re: [PATCH 0/7] KVM: SVM: Enable FRED support

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Message-ID: <85958aa8-98ee-40bc-8fcf-750bbf62ccce@amd.com>
Date: Fri, 6 Feb 2026 14:52:04 +0530
From: Shivansh Dhiman <shivansh.dhiman@....com>
To: <seanjc@...gle.com>, <pbonzini@...hat.com>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
CC: <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
	<xin@...or.com>, <nikunj.dadhania@....com>, <santosh.shukla@....com>,
	Shivansh Dhiman <shivansh.dhiman@....com>
Subject: Re: [PATCH 0/7] KVM: SVM: Enable FRED support

Hi,

Here is the newly published FRED virtualization spec by AMD for reference:

	https://docs.amd.com/v/u/en-US/69191-PUB

Please feel free to share any feedback or questions.

Regards,
Shivansh

On 29-01-2026 12:06, Shivansh Dhiman wrote:
> This series adds SVM support for FRED (Flexible Return and Event Delivery)
> virtualization in KVM.
> 
> FRED introduces simplified privilege level transitions to replace IDT-based
> event delivery and IRET returns, providing lower latency event handling while
> ensuring complete supervisor context on delivery and full user context on
> return. FRED defines event delivery for both ring 3->0 and ring 0->0
> transitions, and introduces ERETU for returning to ring 3 and ERETS for
> remaining in ring 0.
> 
> AMD hardware extends the VMCB to support FRED virtualization with dedicated
> save area fields for FRED MSRs (RSP0-3, SSP1-3, STKLVLS, CONFIG) and control
> fields for event injection data (EXITINTDATA, EVENTINJDATA).
> 
> The implementation spans seven patches. The important changes are:
> 
> 1) Extend VMCB structures with FRED fields mentioned above and disable MSR
>    interception for FRED-enabled guests to avoid unnecessary VM exits.
> 
> 2) Support for nested exceptions where we populate event injection data
>    when delivering exceptions like page faults and debug traps. 
> 
> This series is based on top of FRED support for VMX patchset [1],
> patches 1-17. The VMX patchset was rebased on top of v6.18.0 kernel.
> 
> [1] https://lore.kernel.org/kvm/20251026201911.505204-1-xin@zytor.com
> 
> Regards,
> Shivansh
> ---
> Neeraj Upadhyay (5):
>   KVM: SVM: Initialize FRED VMCB fields
>   KVM: SVM: Disable interception of FRED MSRs for FRED supported guests
>   KVM: SVM: Save restore FRED_RSP0 for FRED supported guests
>   KVM: SVM: Populate FRED event data on event injection
>   KVM: SVM: Support FRED nested exception injection
> 
> Shivansh Dhiman (2):
>   KVM: SVM: Dump FRED context in dump_vmcb()
>   KVM: SVM: Enable save/restore of FRED MSRs
> 
>  arch/x86/include/asm/svm.h |  35 ++++++++++-
>  arch/x86/kvm/svm/svm.c     | 116 +++++++++++++++++++++++++++++++++++--
>  2 files changed, 144 insertions(+), 7 deletions(-)
> 
> 
> base-commit: f76e83ecf6bce6d3793f828d92170b69e636f3c9