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AJvYcCXNnbGDd4WxS7NThVKADfuJ1dx3yjweAJ8+h/jMt40r1/veCIpYBKJIsfw76/Ih/5BadEUcU0qpyagXhDW16GyvyFbQYcc+9D1h1vWu/Aw= X-Gm-Message-State: AOJu0YwdWMAKjHPRm14FIGwmv1ceTXlL2wbKYTc1hBW1MWpKVyn4YmD1 fprfw72ci4FDu2GTLxKuv1IuattcSdNp0X+xQaW8KBjjL4rkCFRA01jVHQu3NsI= X-Google-Smtp-Source: AGHT+IHkmnkjurRVetym/WDZPXA+ZsFtgqHA1M1O5kWuGSQUyXbMYFpjVxVDT40XkMZ6ilPvaHmpXQ== X-Received: by 2002:a05:6512:549:b0:521:cc8a:46dd with SMTP id 2adb3069b0e04-52ca6e56e2dmr2216246e87.11.1718374016080; Fri, 14 Jun 2024 07:06:56 -0700 (PDT) Message-ID: <49313683-fb34-4f6f-a41c-e02ea6837cfd@citrix.com> Date: Fri, 14 Jun 2024 15:06:55 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6/7] x86/cpuid: Fix handling of XSAVE dynamic leaves To: Jan Beulich Cc: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Wei Liu , Xen-devel References: <20240523111627.28896-1-andrew.cooper3@citrix.com> <20240523111627.28896-7-andrew.cooper3@citrix.com> <9e6803c6-3d83-4e5c-a7bd-b8b844eec66d@suse.com> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 23/05/2024 5:16 pm, Jan Beulich wrote: > On 23.05.2024 13:16, Andrew Cooper wrote: >> First, if XSAVE is available in hardware but not visible to the guest, the >> dynamic leaves shouldn't be filled in. >> >> Second, the comment concerning XSS state is wrong. VT-x doesn't manage >> host/guest state automatically, but there is provision for "host only" bits to >> be set, so the implications are still accurate. >> >> Introduce xstate_compressed_size() to mirror the uncompressed one. Cross >> check it at boot. >> >> Signed-off-by: Andrew Cooper > Reviewed-by: Jan Beulich Thanks. > Irrespective ... > >> v3: >> * Adjust commit message about !XSAVE guests >> * Rebase over boot time cross check >> * Use raw policy > ... it should probably have occurred to me earlier on to ask: Why raw policy? > Isn't the host one the more appropriate one to use for any kind of internal > decisions? State information is identical in all policies.  It's the ABI of the X{SAVE,RSTOR}* instructions. Beyond that, consistency. xstate_uncompressed_size() does strictly need to be the raw policy, because it is used by recalculate_xstate() to calculate the host policy. xstate_compressed_size() doesn't have the same restriction, but should use the same source of data. Finally, xstate_{un,}compressed_size() aren't really tied to a choice of features in the first place.  They shouldn't be limited to the host_policy's subset of active features. ~Andrew