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From: Dave Hansen <dave.hansen@intel.com>
To: Tianyu Lan <ltykernel@gmail.com>,
	kys@microsoft.com, haiyangz@microsoft.com,
	sthemmin@microsoft.com, wei.liu@kernel.org, decui@microsoft.com,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com,
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	boris.ostrovsky@oracle.com, jgross@suse.com,
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	michael.h.kelley@microsoft.com
Cc: iommu@lists.linux-foundation.org, linux-arch@vger.kernel.org,
	linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-scsi@vger.kernel.org, netdev@vger.kernel.org,
	vkuznets@redhat.com, anparri@microsoft.com
Subject: Re: [PATCH 03/13] x86/HV: Add new hvcall guest address host visibility support
Date: Thu, 29 Jul 2021 07:09:55 -0700	[thread overview]
Message-ID: <ec1d4cfd-bbbc-e27a-7589-e85d9f0438f4@intel.com> (raw)
In-Reply-To: <0d956a05-7d24-57a0-f4a9-dccc849b52fc@gmail.com>

On 7/29/21 6:01 AM, Tianyu Lan wrote:
> On 7/29/2021 1:06 AM, Dave Hansen wrote:
>> On 7/28/21 7:52 AM, Tianyu Lan wrote:
>>> @@ -1986,7 +1988,9 @@ static int __set_memory_enc_dec(unsigned long
>>> addr, int numpages, bool enc)
>>>       int ret;
>>>         /* Nothing to do if memory encryption is not active */
>>> -    if (!mem_encrypt_active())
>>> +    if (hv_is_isolation_supported())
>>> +        return hv_set_mem_enc(addr, numpages, enc);
>>> +    else if (!mem_encrypt_active())
>>>           return 0;
>>
>> One more thing.  If you're going to be patching generic code, please
>> start using feature checks that can get optimized away at runtime.
>> hv_is_isolation_supported() doesn't look like the world's cheapest
>> check.  It can't be inlined and costs at least a function call.
> 
> Yes, you are right. How about adding a static branch key for the check
> of isolation VM? This may reduce the check cost.

I don't think you need a static key.

There are basically three choices:
1. Use an existing X86_FEATURE bit.  I think there's already one for
   when you are running under a hypervisor.  It's not super precise,
   but it's better than what you have.
2. Define a new X86_FEATURE bit for when you are running under
   Hyper-V.
3. Define a new X86_FEATURE bit specifically for Hyper-V isolation VM
   support.  This particular feature might be a little uncommon to
   deserve its own bit.

I'd probably just do #2.

  reply	other threads:[~2021-07-29 14:12 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-28 14:52 [PATCH 00/13] x86/Hyper-V: Add Hyper-V Isolation VM support Tianyu Lan
2021-07-28 14:52 ` [PATCH 01/13] x86/HV: Initialize GHCB page in Isolation VM Tianyu Lan
2021-08-02 11:53   ` Joerg Roedel
2021-08-02 12:35     ` Tianyu Lan
2021-07-28 14:52 ` [PATCH 02/13] x86/HV: Initialize shared memory boundary in the " Tianyu Lan
2021-07-28 14:52 ` [PATCH 03/13] x86/HV: Add new hvcall guest address host visibility support Tianyu Lan
2021-07-28 15:29   ` Dave Hansen
2021-07-29 12:49     ` Tianyu Lan
2021-08-02 12:01     ` Joerg Roedel
2021-08-02 12:59       ` Tianyu Lan
2021-08-02 13:11       ` Juergen Gross
2021-08-02 13:30         ` Joerg Roedel
2021-07-28 17:06   ` Dave Hansen
2021-07-29 13:01     ` Tianyu Lan
2021-07-29 14:09       ` Dave Hansen [this message]
2021-07-29 15:02         ` Tianyu Lan
2021-07-29 16:05           ` Dave Hansen
2021-07-30  2:52             ` Tianyu Lan
2021-07-28 14:52 ` [PATCH 04/13] HV: Mark vmbus ring buffer visible to host in Isolation VM Tianyu Lan
2021-08-02 12:07   ` Joerg Roedel
2021-08-02 12:56     ` Tianyu Lan
2021-08-02 12:59       ` Joerg Roedel
2021-08-02 13:08         ` Tianyu Lan
2021-07-28 14:52 ` [PATCH 05/13] HV: Add Write/Read MSR registers via ghcb page Tianyu Lan
2021-08-02 12:28   ` Joerg Roedel
2021-08-02 13:18     ` Tianyu Lan
2021-07-28 14:52 ` [PATCH 06/13] HV: Add ghcb hvcall support for SNP VM Tianyu Lan
2021-08-02 12:39   ` Joerg Roedel
2021-08-02 13:32     ` Tianyu Lan
2021-07-28 14:52 ` [PATCH 07/13] HV/Vmbus: Add SNP support for VMbus channel initiate message Tianyu Lan
2021-08-02 12:58   ` Joerg Roedel
2021-07-28 14:52 ` [PATCH 08/13] HV/Vmbus: Initialize VMbus ring buffer for Isolation VM Tianyu Lan
2021-07-28 14:52 ` [PATCH 09/13] DMA: Add dma_map_decrypted/dma_unmap_encrypted() function Tianyu Lan
2021-07-29 15:13   ` Tianyu Lan
2021-07-28 14:52 ` [PATCH 10/13] x86/Swiotlb: Add Swiotlb bounce buffer remap function for HV IVM Tianyu Lan
2021-07-29 16:29   ` Konrad Rzeszutek Wilk
2021-07-30  4:10     ` Tianyu Lan
2021-07-28 14:52 ` [PATCH 11/13] HV/IOMMU: Enable swiotlb bounce buffer for Isolation VM Tianyu Lan
2021-07-28 14:52 ` [PATCH 12/13] HV/Netvsc: Add Isolation VM support for netvsc driver Tianyu Lan
2021-07-28 14:52 ` [PATCH 13/13] HV/Storvsc: Add Isolation VM support for storvsc driver Tianyu Lan
2021-08-02 13:20   ` Joerg Roedel
2021-08-02 14:08     ` Tianyu Lan

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