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Subject: Re: [PATCH 3/6] x86/sev-es: Use __put_user()/__get_user
To:     'Joerg Roedel' <joro@8bytes.org>
Cc:     David Laight <David.Laight@aculab.com>,
        "x86@kernel.org" <x86@kernel.org>,
        Hyunwook Baek <baekhw@google.com>,
        Joerg Roedel <jroedel@suse.de>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "hpa@zytor.com" <hpa@zytor.com>, Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jiri Slaby <jslaby@suse.cz>,
        Dan Williams <dan.j.williams@intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Kees Cook <keescook@chromium.org>,
        David Rientjes <rientjes@google.com>,
        Cfir Cohen <cfir@google.com>,
        Erdem Aktas <erdemaktas@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mike Stunes <mstunes@vmware.com>,
        Sean Christopherson <seanjc@google.com>,
        Martin Radev <martin.b.radev@gmail.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        "linux-coco@lists.linux.dev" <linux-coco@lists.linux.dev>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>
References: <20210512075445.18935-1-joro@8bytes.org>
 <20210512075445.18935-4-joro@8bytes.org>
 <0496626f018d4d27a8034a4822170222@AcuMS.aculab.com>
 <fcb2c501-70ca-1a54-4a75-8ab05c21ee30@suse.com> <YJuW4TtRJKZ+OIhj@8bytes.org>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <92244e37-4443-98bd-24aa-bf59548aab47@suse.com>
Date:   Wed, 12 May 2021 10:58:20 +0200
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From: Juergen Gross <jgross@suse.com>
To: 'Joerg Roedel' <joro@8bytes.org>
Cc: David Laight <David.Laight@aculab.com>, "x86@kernel.org"
 <x86@kernel.org>, Hyunwook Baek <baekhw@google.com>,
 Joerg Roedel <jroedel@suse.de>,
 "stable@vger.kernel.org" <stable@vger.kernel.org>,
 "hpa@zytor.com" <hpa@zytor.com>, Andy Lutomirski <luto@kernel.org>,
 Dave Hansen <dave.hansen@linux.intel.com>,
 Peter Zijlstra <peterz@infradead.org>, Jiri Slaby <jslaby@suse.cz>,
 Dan Williams <dan.j.williams@intel.com>,
 Tom Lendacky <thomas.lendacky@amd.com>, Kees Cook <keescook@chromium.org>,
 David Rientjes <rientjes@google.com>, Cfir Cohen <cfir@google.com>,
 Erdem Aktas <erdemaktas@google.com>, Masami Hiramatsu <mhiramat@kernel.org>,
 Mike Stunes <mstunes@vmware.com>, Sean Christopherson <seanjc@google.com>,
 Martin Radev <martin.b.radev@gmail.com>,
 Arvind Sankar <nivedita@alum.mit.edu>,
 "linux-coco@lists.linux.dev" <linux-coco@lists.linux.dev>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
 "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
 "virtualization@lists.linux-foundation.org"
 <virtualization@lists.linux-foundation.org>
Message-ID: <92244e37-4443-98bd-24aa-bf59548aab47@suse.com>
Subject: Re: [PATCH 3/6] x86/sev-es: Use __put_user()/__get_user
References: <20210512075445.18935-1-joro@8bytes.org>
 <20210512075445.18935-4-joro@8bytes.org>
 <0496626f018d4d27a8034a4822170222@AcuMS.aculab.com>
 <fcb2c501-70ca-1a54-4a75-8ab05c21ee30@suse.com> <YJuW4TtRJKZ+OIhj@8bytes.org>
In-Reply-To: <YJuW4TtRJKZ+OIhj@8bytes.org>

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On 12.05.21 10:50, 'Joerg Roedel' wrote:
> On Wed, May 12, 2021 at 10:16:12AM +0200, Juergen Gross wrote:
>> You want something like xen_safe_[read|write]_ulong().
>=20
>  From a first glance I can't see it, what is the difference between the=

> xen_safe_*_ulong() functions and __get_user()/__put_user()? The only
> difference I can see is that __get/__put_user() support different acces=
s
> sizes, but neither of those disables page-faults by itself, for example=
=2E
>=20
> Couldn't these xen-specific functions not also be replaces by
> __get_user()/__put_user()?

No, those were used before, but commit 9da3f2b7405440 broke Xen's use
case. That is why I did commit 1457d8cf7664f.


Juergen

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