From: Sohil Mehta Date: Mon, 9 Mar 2026 18:10:29 +0000 (-0700) Subject: x86/cpu: Remove LASS restriction on vsyscall emulation X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=584d752b8a1f0ee3a7d5a831e55623c10e7ca0ee;p=thirdparty%2Flinux.git x86/cpu: Remove LASS restriction on vsyscall emulation Vsyscall emulation has two modes of operation: XONLY and EMULATE. The default XONLY mode is now supported with a LASS-triggered #GP. OTOH, LASS is disabled if someone requests the deprecated EMULATE mode via the vsyscall=emulate command line option. So, remove the restriction on LASS when the overall vsyscall emulation support is compiled in. As a result, there is no need for setup_lass() anymore. LASS is enabled by default through a late_initcall(). Signed-off-by: Sohil Mehta Signed-off-by: Dave Hansen Reviewed-by: Dave Hansen Reviewed-by: H. Peter Anvin (Intel) Reviewed-by: Tested-by: Maciej Wieczor-Retman Link: https://patch.msgid.link/20260309181029.398498-6-sohil.mehta@intel.com --- diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 3557f0e6b3aa5..02472fc763d9b 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -406,20 +406,6 @@ out: cr4_clear_bits(X86_CR4_UMIP); } -static __always_inline void setup_lass(struct cpuinfo_x86 *c) -{ - if (!cpu_feature_enabled(X86_FEATURE_LASS)) - return; - - /* - * Legacy vsyscall page access causes a #GP when LASS is active. - * Disable LASS because the #GP handler doesn't support vsyscall - * emulation. - */ - if (IS_ENABLED(CONFIG_X86_VSYSCALL_EMULATION)) - setup_clear_cpu_cap(X86_FEATURE_LASS); -} - static int enable_lass(unsigned int cpu) { cr4_set_bits(X86_CR4_LASS); @@ -2061,7 +2047,6 @@ static void identify_cpu(struct cpuinfo_x86 *c) setup_smep(c); setup_smap(c); setup_umip(c); - setup_lass(c); /* Enable FSGSBASE instructions if available. */ if (cpu_has(c, X86_FEATURE_FSGSBASE)) {