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[46.102.197.194]) by smtp.gmail.com with ESMTPSA id 20-20020a05600c22d400b003f180d5b145sm19957669wmg.40.2023.05.31.02.01.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 31 May 2023 02:01:23 -0700 (PDT) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: b78d825c-ff91-11ed-8611-37d641c3527e DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloud.com; s=cloud; t=1685523683; x=1688115683; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:subject:cc:to:from:date:message-id:from:to :cc:subject:date:message-id:reply-to; bh=qQXWIfDuVmsIWvJfCCkpoHNdEpUjjhn2AgEZ3ftf/xQ=; b=Fl8AxKrsYXzncYC4ObhJR0K2XfnieKzs46piHcvq5aXtYii3Gf7zvI92S2dkVVnuMD hkbCq+UpE/75w+VYzUn5Es/LVpjbYqoArbGZqmMhzI9ivwhOGKiOD2h0kUD8JQPnqxyv M/BfFnL4zCpI5JXntkq7dD/Vi/FvCoxcbqh4I= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1685523683; x=1688115683; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:subject:cc:to:from:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=qQXWIfDuVmsIWvJfCCkpoHNdEpUjjhn2AgEZ3ftf/xQ=; b=eLIVHHC8VpU1Eha7/nBn/0Hh8BocUe0i7OftTbxCMt5truimYR9pLHjM61evx3DXy2 n/0XZt7N8lwCbu0zJyN0WbKSHIPYRRjzBI9bnMY6ZC+9Q8k2gzcx5DgPRxV8yA+bJkwd uxP5UHdndoTq7QQQ0yWLCpibwFhebJccYQqJZCxO6MaZo7aAMUvgbrRYlLTMjanaPNX3 /N22mBjzKGZ1pyd+p6rqjAl2r8EgGe8V27k2uYTNhg8GDeo0fnY4IOQ10C0eoK+kylRw J3kFnIhwL5I20ErW1m6wzzpaNo+HCSMw3NM9Komy4SzhDgKRrGDKhYHFk36Fab7SLO8a p36Q== X-Gm-Message-State: AC+VfDwFXzcOteqfAIviQeIpvT8WbIA7lb8TqZW4he0qjqQeNiADacjA 5Y9k69fF8k5lgSHfvOST4uqp/A== X-Google-Smtp-Source: ACHHUZ4eujNhAr1KbosS0Y71g2yECH5jD8CRv4UNl7qvMDEtgA1r6DkaMn/uODmiUKmlUfBufsGX2g== X-Received: by 2002:a05:600c:20c:b0:3f4:253b:92b3 with SMTP id 12-20020a05600c020c00b003f4253b92b3mr3695636wmi.18.1685523683707; Wed, 31 May 2023 02:01:23 -0700 (PDT) Message-ID: <64770ce3.050a0220.fb998.7ff6@mx.google.com> X-Google-Original-Message-ID: Date: Wed, 31 May 2023 10:01:21 +0100 From: Alejandro Vallejo To: Andrew Cooper Cc: Xen-devel , Jan Beulich , Roger Pau =?iso-8859-1?Q?Monn=E9?= , Wei Liu Subject: Re: [PATCH v2 2/3] x86: Expose Automatic IBRS to guests References: <20230530135854.1517-1-alejandro.vallejo@cloud.com> <20230530135854.1517-3-alejandro.vallejo@cloud.com> <2e1bea58-9f6f-08c0-ce00-148f79ba12ff@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2e1bea58-9f6f-08c0-ce00-148f79ba12ff@citrix.com> On Tue, May 30, 2023 at 06:31:03PM +0100, Andrew Cooper wrote: > I've committed this, but made two tweaks to the commit message.  First, > "x86/hvm" in the subject because it's important context at a glance. Sure, that makes sense. > Second, I've adjusted the bit about PV guests.  The reason why we can't > expose it yet is because Xen doesn't currently context switch EFER > between PV guests. > > ~Andrew We could of course context switch EFER sensibly, but what would that mean for Automatic IBRS? It can't be trivially used for domain-to-domain isolation because every domain is in a co-equal protection level. Is there a non-obvious edge that exposing some interface to it gives for PV? The only useful case I can think of is PVH, and that seems to be subsumed by HVM. Alejandro