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d="scan'208";a="35064265" Subject: Re: [PATCH 1/2] viridian: remove implicit limit of 64 VPs per partition To: Jan Beulich CC: , , , , , , , , , References: <1610066796-17266-1-git-send-email-igor.druzhinin@citrix.com> <62d08bab-6de4-c190-7a8c-910693f16846@suse.com> <4bb15f7f-8e36-1022-0f98-9ce56bd294e6@suse.com> From: Igor Druzhinin Message-ID: <11bc2e42-5c00-2ede-e76e-f5c7af987b7d@citrix.com> Date: Fri, 8 Jan 2021 13:25:18 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <4bb15f7f-8e36-1022-0f98-9ce56bd294e6@suse.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit On 08/01/2021 13:17, Jan Beulich wrote: > On 08.01.2021 12:27, Igor Druzhinin wrote: >> On 08/01/2021 09:19, Jan Beulich wrote: >>> On 08.01.2021 01:46, Igor Druzhinin wrote: >>>> --- a/tools/libs/light/libxl_x86.c >>>> +++ b/tools/libs/light/libxl_x86.c >>>> @@ -336,7 +336,7 @@ static int hvm_set_viridian_features(libxl__gc *gc, uint32_t domid, >>>> LOG(DETAIL, "%s group enabled", libxl_viridian_enlightenment_to_string(v)); >>>> >>>> if (libxl_bitmap_test(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_BASE)) { >>>> - mask |= HVMPV_base_freq; >>>> + mask |= HVMPV_base_freq | HVMPV_no_vp_limit; >>> >>> Could you clarify the point of having the new control when at >>> the guest config level there's no way to prevent it from >>> getting enabled (short of disabling Viridian extensions >>> altogether)? >> >> If you migrate in from a host without this code (previous version >> of Xen)- you will keep the old behavior for the guest thus preserving >> binary compatibility. > > Keeping thing compatible like this is clearly a requirement. But > is this enough? As soon as the guest reboots, it will see differing > behavior, won't it? Yes, that's what I was expecting - after reboot it should be fine. Hence I put this option into the default set - I'd expect no limit to be applied in the first place. Igor