linux-kernel - Re: [PATCH 12/15] KVM: VMX: Reset the bits that are meaningful to be reset in vmx_register_cache

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Message-ID: <b6711c49-edab-acfa-2005-42e4732d0e4f@redhat.com>
Date:   Thu, 18 Nov 2021 16:25:43 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 12/15] KVM: VMX: Reset the bits that are meaningful to be
 reset in vmx_register_cache_reset()

On 11/8/21 13:44, Lai Jiangshan wrote:
> +/*
> + * VMX_REGS_AVAIL_SET - The set of registers that will be updated in cache on
> + *			demand.  Other registers not listed here are synced to
> + *			the cache immediately after VM-Exit.
> + *
> + * VMX_REGS_DIRTY_SET - The set of registers that might be outdated in
> + *			architecture. Other registers not listed here are synced
> + *			to the architecture immediately when modifying.

Slightly more expressive:

/*
  * VMX_REGS_LAZY_LOAD_SET - The set of registers that will be updated in the
  * cache on demand.  Other registers not listed here are synced to
  * the cache immediately after VM-Exit.
  */
...

/*
  * VMX_REGS_LAZY_UPDATE_SET - The set of registers that might be outdated in
  * VMCS. Other registers not listed here are synced to the VMCS
  * immediately when modified.
  */
...

	BUILD_BUG_ON(VMX_REGS_LAZY_UPDATE_SET & ~VMX_REGS_LAZY_LOAD_SET);
         vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
         vcpu->arch.regs_dirty &= ~VMX_REGS_LAZY_UPDATE_SET;

That is lazily loaded registers become unavailable, and lazily updated registers
become unavailable and dirty.

Paolo