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Message-ID: <20251112043730.992152-9-hpa@zytor.com>
Date: Tue, 11 Nov 2025 20:37:26 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: "H. Peter Anvin" <hpa@...or.com>, "Jason A. Donenfeld" <Jason@...c4.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
"Theodore Ts'o" <tytso@....edu>,
Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
Xin Li <xin@...or.com>, Andrew Cooper <andrew.cooper3@...rix.com>,
Andy Lutomirski <luto@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>, James Morse <james.morse@....com>,
Jarkko Sakkinen <jarkko@...nel.org>,
Josh Poimboeuf <jpoimboe@...nel.org>, Kees Cook <kees@...nel.org>,
Nam Cao <namcao@...utronix.de>, Oleg Nesterov <oleg@...hat.com>,
Perry Yuan <perry.yuan@....com>, Thomas Gleixner <tglx@...utronix.de>,
Thomas Huth <thuth@...hat.com>, Uros Bizjak <ubizjak@...il.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-sgx@...r.kernel.org, x86@...nel.org
Subject: [PATCH v2 8/9] x86/cpufeature: replace X86_FEATURE_SYSENTER32 with X86_FEATURE_SYSFAST32
In most cases, the use of "fast 32-bit system call" depends either on
X86_FEATURE_SEP or X86_FEATURE_SYSENTER32 || X86_FEATURE_SYSCALL32.
However, nearly all the logic for both is identical.
Define X86_FEATURE_SYSFAST32 which indicates that *either* SYSENTER32 or
SYSCALL32 should be used, for either 32- or 64-bit kernels. This
defaults to SYSENTER; use SYSCALL if the SYSCALL32 bit is also set.
As this removes ALL existing uses of X86_FEATURE_SYSENTER32, which is
a kernel-only synthetic feature bit, simply remove it and replace it
with X86_FEATURE_SYSFAST32.
This leaves an unused alternative for a true 32-bit kernel, but that
should really not matter in any way.
The clearing of X86_FEATURE_SYSCALL32 can be removed once the patches
for automatically clearing disabled features has been merged.
Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
---
arch/x86/Kconfig.cpufeatures | 8 +++++++
arch/x86/entry/vdso/vdso32/system_call.S | 8 ++-----
arch/x86/include/asm/cpufeatures.h | 2 +-
arch/x86/kernel/cpu/centaur.c | 3 ---
arch/x86/kernel/cpu/common.c | 8 +++++++
arch/x86/kernel/cpu/intel.c | 4 +---
arch/x86/kernel/cpu/zhaoxin.c | 4 +---
arch/x86/kernel/fred.c | 2 +-
arch/x86/xen/setup.c | 28 +++++++++++++++---------
arch/x86/xen/smp_pv.c | 5 ++---
arch/x86/xen/xen-ops.h | 1 -
11 files changed, 42 insertions(+), 31 deletions(-)
diff --git a/arch/x86/Kconfig.cpufeatures b/arch/x86/Kconfig.cpufeatures
index 250c10627ab3..2808b8aee8df 100644
--- a/arch/x86/Kconfig.cpufeatures
+++ b/arch/x86/Kconfig.cpufeatures
@@ -56,6 +56,10 @@ config X86_REQUIRED_FEATURE_MOVBE
def_bool y
depends on MATOM
+config X86_REQUIRED_FEATURE_SYSFAST32
+ def_bool y
+ depends on X86_64 && !X86_FRED
+
config X86_REQUIRED_FEATURE_CPUID
def_bool y
depends on X86_64
@@ -120,6 +124,10 @@ config X86_DISABLED_FEATURE_CENTAUR_MCR
def_bool y
depends on X86_64
+config X86_DISABLED_FEATURE_SYSCALL32
+ def_bool y
+ depends on !X86_64
+
config X86_DISABLED_FEATURE_PCID
def_bool y
depends on !X86_64
diff --git a/arch/x86/entry/vdso/vdso32/system_call.S b/arch/x86/entry/vdso/vdso32/system_call.S
index 2a15634bbe75..7b1c0f16e511 100644
--- a/arch/x86/entry/vdso/vdso32/system_call.S
+++ b/arch/x86/entry/vdso/vdso32/system_call.S
@@ -52,13 +52,9 @@ __kernel_vsyscall:
#define SYSENTER_SEQUENCE "movl %esp, %ebp; sysenter"
#define SYSCALL_SEQUENCE "movl %ecx, %ebp; syscall"
-#ifdef BUILD_VDSO32_64
/* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */
- ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSENTER32, \
- SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32
-#else
- ALTERNATIVE "", SYSENTER_SEQUENCE, X86_FEATURE_SEP
-#endif
+ ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSFAST32, \
+ SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32
/* Enter using int $0x80 */
int $0x80
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 4091a776e37a..f9d1c404b750 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -84,7 +84,7 @@
#define X86_FEATURE_PEBS ( 3*32+12) /* "pebs" Precise-Event Based Sampling */
#define X86_FEATURE_BTS ( 3*32+13) /* "bts" Branch Trace Store */
#define X86_FEATURE_SYSCALL32 ( 3*32+14) /* syscall in IA32 userspace */
-#define X86_FEATURE_SYSENTER32 ( 3*32+15) /* sysenter in IA32 userspace */
+#define X86_FEATURE_SYSFAST32 ( 3*32+15) /* sysenter/syscall in IA32 userspace */
#define X86_FEATURE_REP_GOOD ( 3*32+16) /* "rep_good" REP microcode works well */
#define X86_FEATURE_AMD_LBR_V2 ( 3*32+17) /* "amd_lbr_v2" AMD Last Branch Record Extension Version 2 */
#define X86_FEATURE_CLEAR_CPU_BUF ( 3*32+18) /* Clear CPU buffers using VERW */
diff --git a/arch/x86/kernel/cpu/centaur.c b/arch/x86/kernel/cpu/centaur.c
index a3b55db35c96..9833f837141c 100644
--- a/arch/x86/kernel/cpu/centaur.c
+++ b/arch/x86/kernel/cpu/centaur.c
@@ -102,9 +102,6 @@ static void early_init_centaur(struct cpuinfo_x86 *c)
(c->x86 >= 7))
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
-#ifdef CONFIG_X86_64
- set_cpu_cap(c, X86_FEATURE_SYSENTER32);
-#endif
if (c->x86_power & (1 << 8)) {
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 02d97834a1d4..25af63f0c449 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1049,6 +1049,9 @@ void get_cpu_cap(struct cpuinfo_x86 *c)
init_scattered_cpuid_features(c);
init_speculation_control(c);
+ if (IS_ENABLED(CONFIG_X86_64) || cpu_has(c, X86_FEATURE_SEP))
+ set_cpu_cap(c, X86_FEATURE_SYSFAST32);
+
/*
* Clear/Set all flags overridden by options, after probe.
* This needs to happen each time we re-probe, which may happen
@@ -1794,6 +1797,11 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
* that it can't be enabled in 32-bit mode.
*/
setup_clear_cpu_cap(X86_FEATURE_PCID);
+
+ /*
+ * Never use SYSCALL on a 32-bit kernel
+ */
+ setup_clear_cpu_cap(X86_FEATURE_SYSCALL32);
#endif
/*
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 98ae4c37c93e..646ff33c4651 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -236,9 +236,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
clear_cpu_cap(c, X86_FEATURE_PSE);
}
-#ifdef CONFIG_X86_64
- set_cpu_cap(c, X86_FEATURE_SYSENTER32);
-#else
+#ifndef CONFIG_X86_64
/* Netburst reports 64 bytes clflush size, but does IO in 128 bytes */
if (c->x86 == 15 && c->x86_cache_alignment == 64)
c->x86_cache_alignment = 128;
diff --git a/arch/x86/kernel/cpu/zhaoxin.c b/arch/x86/kernel/cpu/zhaoxin.c
index 89b1c8a70fe8..031379b7d4fa 100644
--- a/arch/x86/kernel/cpu/zhaoxin.c
+++ b/arch/x86/kernel/cpu/zhaoxin.c
@@ -59,9 +59,7 @@ static void early_init_zhaoxin(struct cpuinfo_x86 *c)
{
if (c->x86 >= 0x6)
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
-#ifdef CONFIG_X86_64
- set_cpu_cap(c, X86_FEATURE_SYSENTER32);
-#endif
+
if (c->x86_power & (1 << 8)) {
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
diff --git a/arch/x86/kernel/fred.c b/arch/x86/kernel/fred.c
index 816187da3a47..e736b19e18de 100644
--- a/arch/x86/kernel/fred.c
+++ b/arch/x86/kernel/fred.c
@@ -68,7 +68,7 @@ void cpu_init_fred_exceptions(void)
idt_invalidate();
/* Use int $0x80 for 32-bit system calls in FRED mode */
- setup_clear_cpu_cap(X86_FEATURE_SYSENTER32);
+ setup_clear_cpu_cap(X86_FEATURE_SYSFAST32);
setup_clear_cpu_cap(X86_FEATURE_SYSCALL32);
}
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 3823e52aef52..ac8021c3a997 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -990,13 +990,6 @@ static int register_callback(unsigned type, const void *func)
return HYPERVISOR_callback_op(CALLBACKOP_register, &callback);
}
-void xen_enable_sysenter(void)
-{
- if (cpu_feature_enabled(X86_FEATURE_SYSENTER32) &&
- register_callback(CALLBACKTYPE_sysenter, xen_entry_SYSENTER_compat))
- setup_clear_cpu_cap(X86_FEATURE_SYSENTER32);
-}
-
void xen_enable_syscall(void)
{
int ret;
@@ -1008,11 +1001,27 @@ void xen_enable_syscall(void)
mechanism for syscalls. */
}
- if (cpu_feature_enabled(X86_FEATURE_SYSCALL32) &&
- register_callback(CALLBACKTYPE_syscall32, xen_entry_SYSCALL_compat))
+ if (!cpu_feature_enabled(X86_FEATURE_SYSFAST32))
+ return;
+
+ if (cpu_feature_enabled(X86_FEATURE_SYSCALL32)) {
+ /* Use SYSCALL32 */
+ ret = register_callback(CALLBACKTYPE_syscall32,
+ xen_entry_SYSCALL_compat);
+
+ } else {
+ /* Use SYSENTER32 */
+ ret = register_callback(CALLBACKTYPE_sysenter,
+ xen_entry_SYSENTER_compat);
+ }
+
+ if (ret) {
setup_clear_cpu_cap(X86_FEATURE_SYSCALL32);
+ setup_clear_cpu_cap(X86_FEATURE_SYSFAST32);
+ }
}
+
static void __init xen_pvmmu_arch_setup(void)
{
HYPERVISOR_vm_assist(VMASST_CMD_enable, VMASST_TYPE_writable_pagetables);
@@ -1022,7 +1031,6 @@ static void __init xen_pvmmu_arch_setup(void)
register_callback(CALLBACKTYPE_failsafe, xen_failsafe_callback))
BUG();
- xen_enable_sysenter();
xen_enable_syscall();
}
diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 9bb8ff8bff30..c40f326f0c3a 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -65,10 +65,9 @@ static void cpu_bringup(void)
touch_softlockup_watchdog();
/* PVH runs in ring 0 and allows us to do native syscalls. Yay! */
- if (!xen_feature(XENFEAT_supervisor_mode_kernel)) {
- xen_enable_sysenter();
+ if (!xen_feature(XENFEAT_supervisor_mode_kernel))
xen_enable_syscall();
- }
+
cpu = smp_processor_id();
identify_secondary_cpu(cpu);
set_cpu_sibling_map(cpu);
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 090349baec09..f6c331b20fad 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -60,7 +60,6 @@ phys_addr_t __init xen_find_free_area(phys_addr_t size);
char * __init xen_memory_setup(void);
void __init xen_arch_setup(void);
void xen_banner(void);
-void xen_enable_sysenter(void);
void xen_enable_syscall(void);
void xen_vcpu_restore(void);
--
2.51.1
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