linux-kernel - Re: [PATCH v2 2/7] hyperv: SVM enlightened TLB flush support flag

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Date:   Wed, 21 Apr 2021 13:20:03 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Vineeth Pillai <viremana@...ux.microsoft.com>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Lan Tianyu <Tianyu.Lan@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Paolo Bonzini <pbonzini@...hat.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>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "K. Y. Srinivasan" <kys@...rosoft.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org
Subject: Re: [PATCH v2 2/7] hyperv: SVM enlightened TLB flush support flag

On Wed, Apr 21, 2021 at 07:15:54AM -0400, Vineeth Pillai wrote:
> 
> 
> On 4/21/21 6:00 AM, Wei Liu wrote:
> > On Thu, Apr 15, 2021 at 01:43:37PM +0000, Vineeth Pillai wrote:
> > > +/*
> > > + * This is specific to AMD and specifies that enlightened TLB flush is
> > > + * supported. If guest opts in to this feature, ASID invalidations only
> > > + * flushes gva -> hpa mapping entries. To flush the TLB entries derived
> > > + * from NPT, hypercalls should be used (HvFlushGuestPhysicalAddressSpace
> > > + * or HvFlushGuestPhysicalAddressList).
> > > + */
> > > +#define HV_X64_NESTED_ENLIGHTENED_TLB			BIT(22)
> > > +
> > c
> > This is not yet documented in TLFS, right? I can't find this bit in the
> > latest edition (6.0b).
> This would be documented in the TLFS update which is soon to be
> released.

Okay.

> 
> > 
> > My first thought is the comment says this is AMD specific but the name
> > is rather generic. That looks a bit odd to begin with.
> I thought of of keeping the name generic to avoid renaming Intel
> specific ones also. If I understand correctly, the TLFS would also
> be having generic name for this and just translated the generic
> name here in this header.

Okay. Let's match what is written in TLFS.

Wei.

> 
> Thanks,
> Vineeth
>