linux-kernel - Re: [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP

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Date:   Thu, 12 Apr 2018 18:39:58 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     KarimAllah Ahmed <karahmed@...zon.de>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP_STATE

On 12/04/2018 17:12, KarimAllah Ahmed wrote:
> From: Jim Mattson <jmattson@...gle.com>
> 
> For nested virtualization L0 KVM is managing a bit of state for L2 guests,
> this state can not be captured through the currently available IOCTLs. In
> fact the state captured through all of these IOCTLs is usually a mix of L1
> and L2 state. It is also dependent on whether the L2 guest was running at
> the moment when the process was interrupted to save its state.
> 
> With this capability, there are two new vcpu ioctls: KVM_GET_VMX_STATE and
> KVM_SET_VMX_STATE. These can be used for saving and restoring a VM that is
> in VMX operation.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: x86@...nel.org
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Jim Mattson <jmattson@...gle.com>
> [karahmed@ - rename structs and functions and make them ready for AMD and
>              address previous comments.
>            - rebase & a bit of refactoring.
>            - Merge 7/8 and 8/8 into one patch.
>            - Force a VMExit from L2 after reading the kvm_state to avoid
>              mixed state between L1 and L2 on resurrecting the instance. ]
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
> v2 -> v3:
> - Remove the forced VMExit from L2 after reading the kvm_state. The actual
>   problem is solved.
> - Rebase again!
> - Set nested_run_pending during restore (not sure if it makes sense yet or
>   not).
> - Reduce KVM_REQUEST_ARCH_BASE to 7 instead of 8 (the other alternative is
>   to switch everything to u64)

You still have to rename everything to KVM_{CAP,GET,SET}_NESTED_STATE
(and {vmx_{get,set}_nested state) though. :)

Paolo