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29 Jul 2021 07:09:59 -0700 X-IronPort-AV: E=Sophos;i="5.84,278,1620716400"; d="scan'208";a="581353306" Received: from shuangho-mobl1.amr.corp.intel.com (HELO [10.212.219.154]) ([10.212.219.154]) by fmsmga001-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jul 2021 07:09:57 -0700 Subject: Re: [PATCH 03/13] x86/HV: Add new hvcall guest address host visibility support To: Tianyu Lan , 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, luto@kernel.org, peterz@infradead.org, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com, jgross@suse.com, sstabellini@kernel.org, joro@8bytes.org, will@kernel.org, davem@davemloft.net, kuba@kernel.org, jejb@linux.ibm.com, martin.petersen@oracle.com, arnd@arndb.de, hch@lst.de, m.szyprowski@samsung.com, robin.murphy@arm.com, thomas.lendacky@amd.com, brijesh.singh@amd.com, ardb@kernel.org, Tianyu.Lan@microsoft.com, rientjes@google.com, martin.b.radev@gmail.com, akpm@linux-foundation.org, rppt@kernel.org, kirill.shutemov@linux.intel.com, aneesh.kumar@linux.ibm.com, krish.sadhukhan@oracle.com, saravanand@fb.com, xen-devel@lists.xenproject.org, pgonda@google.com, david@redhat.com, keescook@chromium.org, hannes@cmpxchg.org, sfr@canb.auug.org.au, 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 References: <20210728145232.285861-1-ltykernel@gmail.com> <20210728145232.285861-4-ltykernel@gmail.com> <0d956a05-7d24-57a0-f4a9-dccc849b52fc@gmail.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <0d956a05-7d24-57a0-f4a9-dccc849b52fc@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.