linux-kernel - RE: [PATCH V6 2/5] x86/hyper-v: Add hyperv Isolation VM check in the cc_platform

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Message-ID: <MWHPR21MB1593F014EC440F5DEDCFDDFFD7709@MWHPR21MB1593.namprd21.prod.outlook.com>
Date:   Thu, 9 Dec 2021 20:38:15 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Tianyu Lan <ltykernel@...il.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "hch@...radead.org" <hch@...radead.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>
CC:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        vkuznets <vkuznets@...hat.com>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "hch@....de" <hch@....de>, "joro@...tes.org" <joro@...tes.org>,
        "parri.andrea@...il.com" <parri.andrea@...il.com>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>
Subject: RE: [PATCH V6 2/5] x86/hyper-v: Add hyperv Isolation VM check in the
 cc_platform_has()

From: Tianyu Lan <ltykernel@...il.com> Sent: Monday, December 6, 2021 11:56 PM
> 
> Hyper-V provides Isolation VM which has memory encrypt support. Add
> hyperv_cc_platform_has() and return true for check of GUEST_MEM_ENCRYPT
> attribute.
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> ---
> Change since v3:
> 	* Change code style of checking GUEST_MEM attribute in the
> 	  hyperv_cc_platform_has().
> ---
>  arch/x86/kernel/cc_platform.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kernel/cc_platform.c b/arch/x86/kernel/cc_platform.c
> index 03bb2f343ddb..47db88c275d5 100644
> --- a/arch/x86/kernel/cc_platform.c
> +++ b/arch/x86/kernel/cc_platform.c
> @@ -11,6 +11,7 @@
>  #include <linux/cc_platform.h>
>  #include <linux/mem_encrypt.h>
> 
> +#include <asm/mshyperv.h>
>  #include <asm/processor.h>
> 
>  static bool __maybe_unused intel_cc_platform_has(enum cc_attr attr)
> @@ -58,9 +59,16 @@ static bool amd_cc_platform_has(enum cc_attr attr)
>  #endif
>  }
> 
> +static bool hyperv_cc_platform_has(enum cc_attr attr)
> +{
> +	return attr == CC_ATTR_GUEST_MEM_ENCRYPT;
> +}
> 
>  bool cc_platform_has(enum cc_attr attr)
>  {
> +	if (hv_is_isolation_supported())
> +		return hyperv_cc_platform_has(attr);
> +
>  	if (sme_me_mask)
>  		return amd_cc_platform_has(attr);
> 

Throughout Linux kernel code, there are about 20 calls to cc_platform_has()
with CC_ATTR_GUEST_MEM_ENCRYPT as the argument.  The original code
(from v1 of this patch set) only dealt with the call in sev_setup_arch().   But
with this patch, all the other calls that previously returned "false" will now
return "true" in a Hyper-V Isolated VM.  I didn't try to analyze all these other
calls, so I think there's an open question about whether this is the behavior
we want.

Michael