From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
stefan@agner.ch, Masahiro Yamada <yamada.masahiro@socionext.com>,
Will Deacon <will@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Sasha Levin <sashal@kernel.org>,
sstabellini@kernel.org, James Morris <jmorris@namei.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
xen-devel@lists.xenproject.org,
Vladimir Murzin <vladimir.murzin@arm.com>,
Marc Zyngier <marc.zyngier@arm.com>,
alexios.zavras@intel.com, boris.ostrovsky@oracle.com,
allison@lohutok.net, jgross@suse.com, steve.capper@arm.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
LKML <linux-kernel@vger.kernel.org>,
James Morse <james.morse@arm.com>,
info@metux.net
Subject: Re: [Xen-devel] [PATCH 1/3] arm/arm64/xen: use C inlines for privcmd_call
Date: Fri, 22 Nov 2019 00:53:12 +0000 [thread overview]
Message-ID: <20191122005311.GI25745@shell.armlinux.org.uk> (raw)
In-Reply-To: <CA+CK2bAm0r8zLMz_gdq30zF8io5RzVnbXFSV9NkyT_uUxKJwLA@mail.gmail.com>
On Thu, Nov 21, 2019 at 07:39:22PM -0500, Pavel Tatashin wrote:
> > > That may be, but be very careful that you only use them in ARMv7-only
> > > code. Using them elsewhere is unsafe as the domain register is used
> > > for other purposes, and merely blatting over it (as your
> > > uaccess_enable and uaccess_disable functions do) is unsafe.
> >
> > In fact, I'll turn that into a bit more than a suggestion. I'll make
> > it a NAK on adding them to 32-bit ARM.
> >
>
> That's fine, and I also did not want to change ARM 32-bit. But, do you
> have a suggestion how differentiate between arm64 and arm in
> include/xen/arm/hypercall.h without ugly ifdefs?
Sorry, I don't.
I'm surprised ARM64 doesn't have anything like that, but I suspect
that's because they don't need to do a save/restore type operation.
Whereas, 32-bit ARM does very much need the save/restore behaviour
(although not in this path.)
The problem is, turning uaccess_enable/disable into C code means
that it's open to being used elsewhere in the kernel (ooh, a couple
of useful looking functions that work on both architectures! I can
use that too!) and then we end up with stuff breaking subtly. It's
the potential for subtle breakage that is making me NAK the idea of
adding the inline C functions.
Given the two have diverged, the only answer is ifdefs, sorry.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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next prev parent reply other threads:[~2019-11-22 0:53 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-21 18:48 [Xen-devel] [PATCH 0/3] Use C inlines for uaccess Pavel Tatashin
2019-11-21 18:48 ` [Xen-devel] [PATCH 1/3] arm/arm64/xen: use C inlines for privcmd_call Pavel Tatashin
2019-11-22 0:22 ` Russell King - ARM Linux admin
2019-11-22 0:30 ` Pavel Tatashin
2019-11-22 0:34 ` Russell King - ARM Linux admin
2019-11-22 0:35 ` Russell King - ARM Linux admin
2019-11-22 0:39 ` Pavel Tatashin
2019-11-22 0:53 ` Russell King - ARM Linux admin [this message]
2019-11-21 18:48 ` [Xen-devel] [PATCH 2/3] arm64: remove uaccess_ttbr0 asm macros from cache functions Pavel Tatashin
2019-11-21 18:48 ` [Xen-devel] [PATCH 3/3] arm64: remove the rest of asm-uaccess.h Pavel Tatashin
2019-11-22 1:26 ` Max Filippov
2019-11-22 2:20 ` Pavel Tatashin
2019-11-27 18:44 [Xen-devel] [PATCH 0/3] Use C inlines for uaccess Pavel Tatashin
2019-11-27 18:44 ` [Xen-devel] [PATCH 1/3] arm/arm64/xen: use C inlines for privcmd_call Pavel Tatashin
2019-11-29 15:05 ` Julien Grall
2019-11-29 15:09 ` Andrew Cooper
2019-12-04 17:55 ` Pavel Tatashin
2019-12-04 17:58 ` Pavel Tatashin
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