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From:   Michael Kelley <mikelley@microsoft.com>
To:     Vineeth Pillai <viremana@linux.microsoft.com>,
        Tianyu Lan <Tianyu.Lan@microsoft.com>,
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        Haiyang Zhang <haiyangz@microsoft.com>
CC:     "H. Peter Anvin" <hpa@zytor.com>,
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Subject: RE: [PATCH v5 2/7] hyperv: SVM enlightened TLB flush support flag
Thread-Topic: [PATCH v5 2/7] hyperv: SVM enlightened TLB flush support flag
Thread-Index: AQHXWIs1S0AmjDki9UyNn37L3PaB66sKXwsg
Date:   Tue, 8 Jun 2021 17:04:47 +0000
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 <a060f872d0df1955e52e30b877b3300485edb27c.1622730232.git.viremana@linux.microsoft.com>
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From: Vineeth Pillai <viremana@linux.microsoft.com> Sent: Thursday, June 3,=
 2021 8:15 AM
>=20
> Bit 22 of HYPERV_CPUID_FEATURES.EDX is specific to SVM and specifies
> support for enlightened TLB flush. With this enlightenment enabled,
> ASID invalidations flushes only gva->hpa entries. To flush TLB entries
> derived from NPT, hypercalls should be used

Nit:  Isn't this "must be used"?  "Should be used" sounds slightly optional=
,
and I don't think that's the case.

> (HvFlushGuestPhysicalAddressSpace or HvFlushGuestPhysicalAddressList)
>=20
> Signed-off-by: Vineeth Pillai <viremana@linux.microsoft.com>
> ---
>  arch/x86/include/asm/hyperv-tlfs.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
>=20
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hy=
perv-tlfs.h
> index 606f5cc579b2..005bf14d0449 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -133,6 +133,15 @@
>  #define HV_X64_NESTED_GUEST_MAPPING_FLUSH		BIT(18)
>  #define HV_X64_NESTED_MSR_BITMAP			BIT(19)
>=20
> +/*
> + * 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

Same here regarding "should be used" vs. "must be used".

> + * or HvFlushGuestPhysicalAddressList).
> + */
> +#define HV_X64_NESTED_ENLIGHTENED_TLB			BIT(22)
> +
>  /* HYPERV_CPUID_ISOLATION_CONFIG.EAX bits. */
>  #define HV_PARAVISOR_PRESENT				BIT(0)
>=20
> --
> 2.25.1

Reviewed-by: Michael Kelley <mikelley@microsoft.com>