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.
