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From: 'Joerg Roedel' <joro@8bytes.org>
To: David Laight <David.Laight@aculab.com>
Cc: "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>,
	Juergen Gross <jgross@suse.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>
Subject: Re: [PATCH 3/6] x86/sev-es: Use __put_user()/__get_user
Date: Wed, 12 May 2021 10:37:34 +0200	[thread overview]
Message-ID: <YJuTzhSp2XAJIYlv@8bytes.org> (raw)
In-Reply-To: <0496626f018d4d27a8034a4822170222@AcuMS.aculab.com>

On Wed, May 12, 2021 at 08:04:33AM +0000, David Laight wrote:
> That can't be right at all.
> __put/get_user() are only valid on user addresses and will try to
> fault in a missing page - so can sleep.

Yes, in general these functions can sleep, but not in this context. They
are called in atomic context and the page-fault handler will notice that
and goes down the __bad_area_nosemaphore() path and only do the fixup.

I also thought about adding page_fault_disable()/page_fault_enable()
calls, but being in atomic context is enough according to the
faulthandler_disabled() implementation.

This is exactly what is needed here. All I want to know is whether a
fault happened or not, the page-fault handler must not try to fix the
fault in any way. If a fault happens it is later fixed up in
vc_forward_exception().

> At best this is abused the calls.

Yes, but that is only due to the naming of these functions. In this case
they do exactly what is needed.

Regards,

	Joerg

  parent reply	other threads:[~2021-05-12  8:37 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-12  7:54 [PATCH 0/6] x86/sev-es: Fixes for SEV-ES guest support Joerg Roedel
2021-05-12  7:54 ` [PATCH 1/6] x86/sev-es: Don't return NULL from sev_es_get_ghcb() Joerg Roedel
2021-05-12  7:54 ` [PATCH 2/6] x86/sev-es: Forward page-faults which happen during emulation Joerg Roedel
2021-05-12 17:31   ` Sean Christopherson
2021-05-19 13:16     ` Joerg Roedel
2021-05-12  7:54 ` [PATCH 3/6] x86/sev-es: Use __put_user()/__get_user Joerg Roedel
2021-05-12  8:04   ` David Laight
2021-05-12  8:16     ` Juergen Gross
2021-05-12  8:50       ` 'Joerg Roedel'
2021-05-12  8:58         ` Juergen Gross
2021-05-12  9:31           ` David Laight
2021-05-12  9:32           ` Joerg Roedel
2021-05-19 11:33             ` 'Joerg Roedel'
2021-05-12  8:37     ` 'Joerg Roedel' [this message]
2021-05-12 15:59       ` Dave Hansen
2021-05-12 15:57   ` Dave Hansen
2021-05-12 16:00     ` Joerg Roedel
2021-05-12  7:54 ` [PATCH 4/6] Revert "x86/sev-es: Handle string port IO to kernel memory properly" Joerg Roedel
2021-05-12 17:38   ` Sean Christopherson
2021-05-19 12:22     ` Joerg Roedel
2021-05-12  7:54 ` [PATCH 5/6] x86/sev-es: Fix error message in runtime #VC handler Joerg Roedel
2021-05-12  7:54 ` [PATCH 6/6] x86/sev-es: Leave NMI-mode before sending signals Joerg Roedel

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