From mboxrd@z Thu Jan 1 00:00:00 1970 From: marc.zyngier@arm.com (Marc Zyngier) Date: Wed, 27 Nov 2013 17:59:41 +0000 Subject: [RFC PATCH 0/2] arm64: Add support for 48-bit Physical Addresses In-Reply-To: References: <1385537665-5909-1-git-send-email-mohun106@gmail.com> <5295D1A5.5090403@arm.com> Message-ID: <5296330D.9010801@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 27/11/13 15:33, Radha Mohan wrote: > On Wed, Nov 27, 2013 at 4:34 PM, Marc Zyngier wrote: >> [CC-ing the maintainers - seems odd they were not cc-ed the first place] >> >> On 27/11/13 07:34, mohun106 at gmail.com wrote: >>> From: Radha Mohan Chintakuntla >>> >>> This patch series provides an implementation of supporting 48-bit >>> Physical Addresses for ARMv8 platforms. It is the maximum width that >>> any ARMv8 based processor can support. >>> >>> The implementation extends the existing support of 40-bit PA.The kernel >>> and user space will now be able to access 128TB each. With 4KB page size >>> the Linux now will be using 4 levels of page tables by making use of >>> 'pud'. And with 64KB page size the Linux will be using 3 levels of page >>> tables. >>> >>> The code has been tested with LTP. >> >> Aside from finding out whether or not this is a useful change, this >> breaks KVM, more specifically the way kernel pages are mapped into HYP. >> Also, guests will still be limited to 40-bit IPAs, and the stage-2 >> output range needs to be addressed as well. > > This is useful for platforms (like ours) that will use 48-bit PAs. > Sooner or later there will > be such processors. So should the 4-level page table cost be unconditionally forced onto all implementations? > And yes, I haven't checked on KVM. Yeah, tiny detail... ;-) M. -- Jazz is not dead. It just smells funny...