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mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.onmicrosoft.com; s=selector2-citrix-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=J34mvslvyE2BkQ5cxj3q/tvzkRJ4tyApqnGhdsNAF4Q=; b=hBlAbWBPktfba4aOKtdqTgg6O3ybrD7QUOFw8GYiaEWBcgmXQP+rsLjxxek2NcRMCJ5OeLEg5ms36+waI0uVbfaz3TENLikW4PX3h4gKSt7qn2xnCUtczNFcVbPHgwbOXYtWJqELaN2cQjdMUd/pLl60WFJqpWi3pA0+4IwIs2s= From: Andrew Cooper To: Jan Beulich CC: George Dunlap , Ian Jackson , Julien Grall , Stefano Stabellini , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , "xen-devel@lists.xenproject.org" References: <322de6db-e01f-0b57-5777-5d94a13c441a@suse.com> <8ba8f016-0aed-277b-bbea-80022d057791@suse.com> <5a954be8-e213-36d8-27da-4c51243dc280@citrix.com> Subject: Re: [PATCH v3 03/22] x86/xstate: re-size save area when CPUID policy changes Message-ID: Date: Tue, 11 May 2021 17:41:54 +0100 User-Agent: Mozilla/5.0 (X11; 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X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?N0tFeldZZ2N5cVZOYnFXdkJobW9vRHhjTVFFUjVvR2NFTVd0NE9GNXBKVFBD?= =?utf-8?B?aGphV0p2bjV0UEYzTnZOamdpM0szMDBoK2RQbFJCZEp1YnlLbGdFQ2dTZGk3?= =?utf-8?B?NElheHRJZ3J5QmUvNTcrT2FzMldYblhRazcxQldCUWUrUmxxQ2p4R0kzcVAr?= =?utf-8?B?UmNFdnhZUytncXAvUldEcjI4MEtyOGkwNTRic0NFbkZNdXdOUFAwZEkzbFN5?= =?utf-8?B?TDE0MjY5WEFRaTV5NEdSaWNZZnZVbGpscWptSk0rOEVvUVlQcFNSU0RoKzRP?= =?utf-8?B?bzZkL2lNZklkWEE1SGVZMWVZMnlocUliTVd1UVo3SWV6Ni9KVnNjejVPQk54?= =?utf-8?B?UGFLUlhyWFpBN3lDS2JweXprdldVdGxQMlhiSVlNOXRNM2RBQVFzVUpLRk51?= =?utf-8?B?VnFpUkhoUm5VdDJiVWRka1BCWlhRdElxY21CK2YrUzU1alMyOW9BeWpiTTFk?= =?utf-8?B?YWRQK1JFdStPcnB3c0V1ZDVPZkpST1Z0UXdld2pYWmc0Q20weWF1b1Z6c0Jv?= =?utf-8?B?K2ZNdklTOFBpNGpMYUIxU05YeGQ2WmJ5TzBrUEx1VWZXRXhEZUNsTVNDNEsz?= =?utf-8?B?VmU4ZytITzRDYXlrQnYyUUNHVjhBRDBqMEc0ZmEvYk1wMlZDRk1uWlZRS0VX?= =?utf-8?B?UlM2VndaUjUxSndzSk04OXppL2ZJVGZHVmJjVjU5Yk9WMUFGMWtORmlYWk54?= =?utf-8?B?c0FZUXZ5K0ZwVFNoTWlSdzExWEtWSmJZZ1NpTWdjOCthc3MwMG1kVE9FaGlB?= =?utf-8?B?NzY1Y3FMWE9xRHY5cGswZjhBSHpCNEFTZ1c0akk3clN4TkJlNXVDckd6M1E1?= =?utf-8?B?ajFtTW1JR094WFgrYjE0ejIxbzNoKzNwVk1hR3pJNGwxcmZvSjN3RzFRT1pX?= =?utf-8?B?ZGRGS3VDcVptbmpwTkcyS1FIaitSMkNGVWFVbVVwMzdSWjl3Z1NaR3BPdkQ3?= =?utf-8?B?N3pxa2VBcTVHdDBrcFN5dThEdWFZZDNibzBVS0t0SnRUSlBHbjJTNGE1SGFT?= =?utf-8?B?ZGRINFN2bko4UXBWVVZicWNBZWJBdjI3UUl4RW9VazFnOVJ6dk85UEpEeEth?= =?utf-8?B?b3FOTzMzZ3FBT2ZVVWh5WEVId0F1L3U5OEc4UWJUYjYwM3Z3d1hNUWk3Z0JP?= =?utf-8?B?SWRCUSt5ZFFEQk1XZkE0eGU5N2pDTEwxUVZEeUJ3VHpnUzUzYjV1MkJzYkFE?= =?utf-8?B?VGhUMmozK3g2eE1tRU9wWFJWeG1LUEd2bVdKVVVZTmdhbE16ZU8rOEVXVkw1?= =?utf-8?B?WmJXWkx6MGxEeUViQTBwTERYU1Y5VnB4Szk3bVlsalk3TGlBTnI2RU44aFBz?= =?utf-8?B?bmsvK2FGTXQ0dGpzcEk1QlBGa0xDMFUwU1JScldFdWN1ZHVuMXBRWk9vNmgy?= =?utf-8?B?V0VKQlRRczhkcmZhVlFPVTJac0JyenhMVGNQbDQ2Y2NTNlIwWCtBcW1kbDYr?= =?utf-8?B?dHZwYWlCdXNXeEhmTGhNY2UvUC83bTNOQWM4bWl1NGl4MkhYcHVWblQxUHFS?= =?utf-8?B?bHdqVTBGVlhOV3JzUlI4L2FJbWhmVEwrdlBJc3ZWc3YzL0ErNWdjNHFJVFpj?= =?utf-8?B?R0hidlBuN1g0MGh4U1FJam50aEl6V1F3eFZHVm9VaXR0VE1ET3JzNlYxcUx5?= =?utf-8?B?MnVyckw3RlM2ZEFXMnUxMzhtME5LdDhwZTRxTHVZclZaK0MzUFBVb21HQi9Z?= =?utf-8?B?S2hTTGVwaDJZY1ZUM3YwR3Fmc0JCUUhMQW1LV2FWbWtaYnB1c2ptdTU4VjBK?= =?utf-8?Q?qbnY5+lTdyonQjsB17geFzsff1ZnH7G4PVlZn4B?= X-MS-Exchange-CrossTenant-Network-Message-Id: 640a0976-1a9b-452f-1601-08d9149bb3f1 X-MS-Exchange-CrossTenant-AuthSource: BYAPR03MB3623.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 May 2021 16:42:02.3442 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 335836de-42ef-43a2-b145-348c2ee9ca5b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: s+t4vTlRn1J3TswnQviXoioibxoaID57WhNtVQBh8iLN5rb//KpAFwofinYtohIoFJoxsPR97UjJWJmds/RketuSOwlWEXqep/dcVqvO89c= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR03MB3429 X-OriginatorOrg: citrix.com On 03/05/2021 15:22, Jan Beulich wrote: >> Another consequence is that we need to rethink our hypercall behaviour.= =C2=A0 >> There is no such thing as supervisor states in an uncompressed XSAVE >> image, which means we can't continue with that being the ABI. > I don't think the hypercall input / output blob needs to follow any > specific hardware layout. Currently, the blob is { xcr0, xcr0_accum, uncompressed image }. As we haven't supported any compressed states yet, we are at liberty to create a forward compatible change by logically s/xcr0/xstate/ and permitting an uncompressed image. Irritatingly, we have xcr0=3D0 as a permitted state and out in the field, for "no xsave state".=C2=A0 This contributes a substantial quantity of complexity in our xstate logic, and invalidates the easy fix I had for not letting the HVM initpath explode. The first task is to untangle the non-architectural xcr0=3D0 case, and to support compressed images.=C2=A0 Size parsing needs to be split into two, a= s for compressed images, we need to consume XSTATE_BV and XCOMP_BV to cross-check the size. I think we also want a rule that Xen will always send compressed if it is using XSAVES (/XSAVEC in the interim?)=C2=A0 We do not want to be workin= g with uncompressed images at all, now that MPX is a reasonable sized hole in the middle. Cleaning this up will then unblock v2 of the existing xstate cleanup series I posted. >> In terms of actual context switching, we want to be using XSAVES/XRSTORS >> whenever it is available, even if we're not using supervisor states.=C2= =A0 >> XSAVES has both the inuse and modified optimisations, without the broken >> consequence of XSAVEOPT (which is firmly in the "don't ever use this" >> bucket now). > The XSAVEOPT anomaly is affecting user mode only, isn't it? Or are > you talking of something I have forgot about? It's not safe to use at all in L1 xen, because the tracking leaks between non-root contexts.=C2=A0 I can't remember if there are further problems for an L0 xen, but I have a nagging feeling that there is. ~Andrew