linux-kernel - Re: [PATCH v3 6/6] arm64/mm: Drop configurable 48-bit physical address space limit

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Message-ID: <20241221121054.GA27495@willie-the-truck>
Date: Sat, 21 Dec 2024 12:10:55 +0000
From: Will Deacon <will@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Ard Biesheuvel <ardb+git@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Ard Biesheuvel <ardb@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>,
	Ryan Roberts <ryan.roberts@....com>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Kees Cook <keescook@...omium.org>,
	Quentin Perret <qperret@...gle.com>
Subject: Re: [PATCH v3 6/6] arm64/mm: Drop configurable 48-bit physical
 address space limit

On Fri, Dec 20, 2024 at 05:29:06PM -0700, Nathan Chancellor wrote:
> On Thu, Dec 12, 2024 at 09:18:48AM +0100, Ard Biesheuvel wrote:
> > From: Ard Biesheuvel <ardb@...nel.org>
> > 
> > Currently, the maximum supported physical address space can be
> > configured as either 48 bits or 52 bits. The only remaining difference
> > between these in practice is that the former omits the masking and
> > shifting required to construct TTBR and PTE values, which carry bits #48
> > and higher disjoint from the rest of the physical address.
> > 
> > The overhead of performing these additional calculations is negligible,
> > and so there is little reason to retain support for two different
> > configurations, and we can simply support whatever the hardware
> > supports.
> 
> I am seeing a boot failure after this change as commit 32d053d6f5e9
> ("arm64/mm: Drop configurable 48-bit physical address space limit") in
> next-20241220 with several distribution configurations that all set
> ARM64_VA_BITS_48. I can reproduce it on bare metal and in QEMU. Simply:

We dropped the patch yesterday, so hopefully things are better today.

Sorry for the bother and thanks for the report,

Will