From mboxrd@z Thu Jan 1 00:00:00 1970 From: ard.biesheuvel@linaro.org (Ard Biesheuvel) Date: Wed, 29 Jul 2015 21:51:15 +0200 Subject: [RFC] arm64: defconfig: enable 48-bit VA by default In-Reply-To: References: <55B0E1AD.60409@arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 29 July 2015 at 21:27, Stuart Yoder wrote: > >> -----Original Message----- >> From: Marc Zyngier [mailto:marc.zyngier at arm.com] >> Sent: Thursday, July 23, 2015 7:44 AM >> To: Yoder Stuart-B08248; Catalin Marinas; Will Deacon >> Cc: linux-arm-kernel at lists.infradead.org; Newton Peter-RA3823 >> Subject: Re: [RFC] arm64: defconfig: enable 48-bit VA by default >> >> On 22/07/15 20:49, Stuart Yoder wrote: >> > Catalin/Will, >> > >> > This is not a patch mean to be applied, but a query about whether there >> > is any reason to not enable 48-bit VA by default in the arm64 defconfig. >> > >> > The Freescale LS2085A physical memory map requires 48-bit VA in Linux for the >> > reasons mentioned in [1]. >> > >> > Based on the comment in [1] by Catalin, it seems that the intent >> > is to turn this on by default. >> > >> > Is there any issues anyone sees with a patch that does this: >> > >> > diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig >> > index 4e17e7e..5acf75d 100644 >> > @@ -47,6 +47,7 @@ CONFIG_ARCH_ZYNQMP=y >> > CONFIG_PCI=y >> > CONFIG_PCI_MSI=y >> > CONFIG_PCI_XGENE=y >> > +CONFIG_ARM64_VA_BITS_48=y >> > CONFIG_SMP=y >> > CONFIG_PREEMPT=y >> > CONFIG_KSM=y >> > >> > Thanks, >> > Stuart >> > >> > [1] https://www.marc.info/?l=linux-arm-kernel&m=140965303205473&w=1 >> > >> >> Is that still a requirement now that our idmap can use 4 levels (as part >> of dd006da)? > > So, yes it appears still to be a requirement. The idmap support is not > the issue, it's the linear mapping. > > Has there been discussion or thinking about enabling 48-bit VA in the > default defconfig? As mentioned before, it seemed that supporting 48-bit > VA was the planned default (~1 year ago), and was waiting on KVM issues to get > resolved. > > A related question is what the thinking around enabling 64KB pages > by default. Any chance of that happening? > > I would like to see our platform work with the default defconfig, which > is the reason for the questions. > Perhaps you should mention, for the benefit of those not following the other thread, that the platform in question has 2 chunks of memory, i.e., 2 GB and 14 GB, with a 508 GB hole in between. To be honest, I think this is poorly designed, and I am not sure we should cater for such configurations in the defconfig. Regards, Ard.