On 9/30/2024 10:00 PM, Xin Li (Intel) wrote:
This patch set enables the Intel flexible return and event delivery
(FRED) architecture with KVM VMX to allow guests to utilize FRED.
The FRED architecture defines simple new transitions that change
privilege level (ring transitions). The FRED architecture was
designed with the following goals:
1) Improve overall performance and response time by replacing event
delivery through the interrupt descriptor table (IDT event
delivery) and event return by the IRET instruction with lower
latency transitions.
2) Improve software robustness by ensuring that event delivery
establishes the full supervisor context and that event return
establishes the full user context.
The new transitions defined by the FRED architecture are FRED event
delivery and, for returning from events, two FRED return instructions.
FRED event delivery can effect a transition from ring 3 to ring 0, but
it is used also to deliver events incident to ring 0. One FRED
instruction (ERETU) effects a return from ring 0 to ring 3, while the
other (ERETS) returns while remaining in ring 0. Collectively, FRED
event delivery and the FRED return instructions are FRED transitions.
Intel VMX architecture is extended to run FRED guests, and the major
changes are:
1) New VMCS fields for FRED context management, which includes two new
event data VMCS fields, eight new guest FRED context VMCS fields and
eight new host FRED context VMCS fields.
2) VMX nested-exception support for proper virtualization of stack
levels introduced with FRED architecture.
Search for the latest FRED spec in most search engines with this search
pattern:
site:intel.com FRED (flexible return and event delivery) specification
The first 20 patches add FRED support to VMX, and the rest 7 patches
add FRED support to nested VMX.
Following is the link to the v2 of this patch set:
https://lore.kernel.org/kvm/20240207172646.3981-1-xin3.li@xxxxxxxxx/
Sean Christopherson (3):
KVM: x86: Use a dedicated flow for queueing re-injected exceptions
KVM: VMX: Don't modify guest XFD_ERR if CR0.TS=1
KVM: VMX: Pass XFD_ERR as pseudo-payload when injecting #NM
Xin Li (21):
KVM: VMX: Add support for the secondary VM exit controls
KVM: VMX: Initialize FRED VM entry/exit controls in vmcs_config
KVM: VMX: Disable FRED if FRED consistency checks fail
KVM: VMX: Initialize VMCS FRED fields
KVM: x86: Use KVM-governed feature framework to track "FRED enabled"
KVM: VMX: Set FRED MSR interception
KVM: VMX: Save/restore guest FRED RSP0
KVM: VMX: Add support for FRED context save/restore
KVM: x86: Add a helper to detect if FRED is enabled for a vCPU
KVM: VMX: Virtualize FRED event_data
KVM: VMX: Virtualize FRED nested exception tracking
KVM: x86: Mark CR4.FRED as not reserved when guest can use FRED
KVM: VMX: Dump FRED context in dump_vmcs()
KVM: x86: Allow FRED/LKGS to be advertised to guests
KVM: x86: Allow WRMSRNS to be advertised to guests
KVM: VMX: Invoke vmx_set_cpu_caps() before nested setup
KVM: nVMX: Add support for the secondary VM exit controls
KVM: nVMX: Add a prerequisite to SHADOW_FIELD_R[OW] macros
KVM: nVMX: Add FRED VMCS fields
KVM: nVMX: Add VMCS FRED states checking
KVM: nVMX: Allow VMX FRED controls
Xin Li (Intel) (3):
x86/cea: Export per CPU variable cea_exception_stacks
KVM: VMX: Do not use MAX_POSSIBLE_PASSTHROUGH_MSRS in array definition
KVM: nVMX: Add a prerequisite to existence of VMCS fields
Hi Sean,
While I'm waiting for the CET patches for native Linux and KVM to be
upstreamed, do you think if it's worth it for you to take the cleanup
and some of the preparation patches first?
Top of my mind are:
KVM: x86: Use a dedicated flow for queueing re-injected exceptions
KVM: VMX: Don't modify guest XFD_ERR if CR0.TS=1
KVM: VMX: Pass XFD_ERR as pseudo-payload when injecting #NM
KVM: nVMX: Add a prerequisite to existence of VMCS fields
KVM: nVMX: Add a prerequisite to SHADOW_FIELD_R[OW] macros
Then specially, the nested exception tracking patch seems a good one as
Chao Gao suggested to decouple the nested tracking from FRED:
KVM: VMX: Virtualize nested exception tracking
Lastly the patches to add support for the secondary VM exit controls
might go in early as well:
KVM: VMX: Add support for the secondary VM exit controls
KVM: nVMX: Add support for the secondary VM exit controls
But if you don't like the idea please just let me know.
Thanks!
Xin
