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Date: Fri, 22 Nov 2019 00:53:12 +0000 From: Russell King - ARM Linux admin <linux@...linux.org.uk> To: Pavel Tatashin <pasha.tatashin@...een.com> Cc: Mark Rutland <mark.rutland@....com>, Catalin Marinas <catalin.marinas@....com>, stefan@...er.ch, Masahiro Yamada <yamada.masahiro@...ionext.com>, Will Deacon <will@...nel.org>, boris.ostrovsky@...cle.com, Sasha Levin <sashal@...nel.org>, sstabellini@...nel.org, James Morris <jmorris@...ei.org>, Linux ARM <linux-arm-kernel@...ts.infradead.org>, xen-devel@...ts.xenproject.org, Vladimir Murzin <vladimir.murzin@....com>, Marc Zyngier <marc.zyngier@....com>, alexios.zavras@...el.com, Thomas Gleixner <tglx@...utronix.de>, allison@...utok.net, jgross@...e.com, steve.capper@....com, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, LKML <linux-kernel@...r.kernel.org>, James Morse <james.morse@....com>, info@...ux.net Subject: Re: [PATCH 1/3] arm/arm64/xen: use C inlines for privcmd_call 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/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up
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