linux-kernel - [PATCH] x86/boot: Move x86_cache_alignment initialization to correct spot

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Date:   Mon,  2 Oct 2023 15:00:45 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org, nathan@...nel.org
Cc:     x86@...nel.org, acdunlap@...gle.com, ashok.raj@...el.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, david@...hat.com,
        dionnaglaze@...gle.com, hpa@...or.com, jacobhxu@...gle.com,
        jgross@...e.com, jroedel@...e.de, khalid.elmously@...onical.com,
        kim.phillips@....com, kirill.shutemov@...ux.intel.com,
        llvm@...ts.linux.dev, luto@...nel.org, mingo@...hat.com,
        nikunj@....com, peterz@...radead.org, pgonda@...gle.com,
        rientjes@...gle.com, rppt@...nel.org, seanjc@...gle.com,
        tglx@...utronix.de, thomas.lendacky@....com,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH] x86/boot: Move x86_cache_alignment initialization to correct spot

c->x86_cache_alignment is initialized from c->x86_clflush_size.
However, commit fbf6449f84bf moved c->x86_clflush_size initialization
to later in boot without moving the c->x86_cache_alignment assignment.

This presumably left c->x86_cache_alignment set to zero for longer
than it should be.

The result was an oops on 32-bit kernels while accessing a pointer
at 0x20.  The 0x20 came from accessing a structure member at offset
0x10 (buffer->cpumask) from a ZERO_SIZE_PTR=0x10.  kmalloc() can
evidently return ZERO_SIZE_PTR when it's given 0 as its alignment
requirement.

Move the c->x86_cache_alignment initialization to be after
c->x86_clflush_size has an actual value.

Fixes: fbf6449f84bf ("x86/sev-es: Set x86_virt_bits to the correct value straight away, instead of a two-phase approach")
Cc: Adam Dunlap <acdunlap@...gle.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Jacob Xu <jacobhxu@...gle.com>
Link: https://lore.kernel.org/all/20231002200426.GA4127272@dev-arch.thelio-3990X/
---
 arch/x86/kernel/cpu/common.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 8d7063e4f63c9..9c51ad5bbf319 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1141,6 +1141,7 @@ void get_cpu_address_sizes(struct cpuinfo_x86 *c)
 		}
 	}
 	c->x86_cache_bits = c->x86_phys_bits;
+	c->x86_cache_alignment = c->x86_clflush_size;
 }
 
 static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
@@ -1594,8 +1595,6 @@ static void __init cpu_parse_early_param(void)
  */
 static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 {
-	c->x86_cache_alignment = c->x86_clflush_size;
-
 	memset(&c->x86_capability, 0, sizeof(c->x86_capability));
 	c->extended_cpuid_level = 0;
 
-- 
2.34.1