linux-kernel - [tip: x86/urgent] x86/mm: Fix early boot use of INVPLGB

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <175020383660.406.12562669775313990568.tip-bot2@tip-bot2>
Date: Tue, 17 Jun 2025 23:43:56 -0000
From: "tip-bot2 for Rik van Riel" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Rik van Riel <riel@...riel.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/mm: Fix early boot use of INVPLGB

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     cb6075bc62dc6a9cd7ab3572758685fdf78e3e20
Gitweb:        https://git.kernel.org/tip/cb6075bc62dc6a9cd7ab3572758685fdf78e3e20
Author:        Rik van Riel <riel@...riel.com>
AuthorDate:    Fri, 06 Jun 2025 13:10:34 -04:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Tue, 17 Jun 2025 16:36:58 -07:00

x86/mm: Fix early boot use of INVPLGB

The INVLPGB instruction has limits on how many pages it can invalidate
at once. That limit is enumerated in CPUID, read by the kernel, and
stored in 'invpgb_count_max'. Ranged invalidation, like
invlpgb_kernel_range_flush() break up their invalidations so
that they do not exceed the limit.

However, early boot code currently attempts to do ranged
invalidation before populating 'invlpgb_count_max'. There is a
for loop which is basically:

	for (...; addr < end; addr += invlpgb_count_max*PAGE_SIZE)

If invlpgb_kernel_range_flush is called before the kernel has read
the value of invlpgb_count_max from the hardware, the normally
bounded loop can become an infinite loop if invlpgb_count_max is
initialized to zero.

Fix that issue by initializing invlpgb_count_max to 1.

This way INVPLGB at early boot time will be a little bit slower
than normal (with initialized invplgb_count_max), and not an
instant hang at bootup time.

Fixes: b7aa05cbdc52 ("x86/mm: Add INVLPGB support code")
Signed-off-by: Rik van Riel <riel@...riel.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Link: https://lore.kernel.org/all/20250606171112.4013261-3-riel%40surriel.com
---
 arch/x86/kernel/cpu/amd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 93da466..b2ad8d1 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -31,7 +31,7 @@

 #include "cpu.h"

-u16 invlpgb_count_max __ro_after_init;
+u16 invlpgb_count_max __ro_after_init = 1;

 static inline int rdmsrq_amd_safe(unsigned msr, u64 *p)
 {