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Date: Mon, 1 Apr 2024 10:56:14 -0700 From: Dave Hansen <dave.hansen@...el.com> To: Javier Pello <devel@...eo.eu>, linux-kernel@...r.kernel.org Cc: x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com> Subject: Re: [PATCH 1/1] x86/mm/pae: Align up pteval_t, pmdval_t and pudval_t to avoid split locks On 4/1/24 09:57, Javier Pello wrote: > -typedef u64 pteval_t; > -typedef u64 pmdval_t; > -typedef u64 pudval_t; > -typedef u64 p4dval_t; > -typedef u64 pgdval_t; > -typedef u64 pgprotval_t; > +/* > + * Variables of these types are subject to atomic compare-and-exchange > + * operations, so they have to be properly aligned to avoid split locks. > + */ > +typedef u64 pteval_t __aligned(8); > +typedef u64 pmdval_t __aligned(8); > +typedef u64 pudval_t __aligned(8); > +typedef u64 p4dval_t __aligned(8); > +typedef u64 pgdval_t __aligned(8); > +typedef u64 pgprotval_t __aligned(8); First of all, how is it that you're running a PAE kernel on new, 64-bit hardware? That's rather odd. The case that you're hitting is actually an on-stack pmd_t. The fun part is that it's not shared and doesn't even _need_ atomics. I think it's just using pmd_populate() because it's convenient. I'd honestly much rather just disable split lock support in 32-bit builds than mess with this stuff. You really shouldn't be running 32-but kernels on this hardware.
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