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Message-Id: <20230702194020.1776895-2-sashal@kernel.org>
Date: Sun, 2 Jul 2023 15:40:07 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
David Woodhouse <dwmw@...zon.co.uk>,
Peter Zijlstra <peterz@...radead.org>,
Michael Kelley <mikelley@...rosoft.com>,
Oleksandr Natalenko <oleksandr@...alenko.name>,
Helge Deller <deller@....de>,
"Guilherme G . Piccoli" <gpiccoli@...lia.com>,
Sasha Levin <sashal@...nel.org>, mingo@...hat.com,
bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
usama.arif@...edance.com, brgerst@...il.com, jgross@...e.com,
jpoimboe@...nel.org, thomas.lendacky@....com
Subject: [PATCH AUTOSEL 6.4 02/15] x86/smpboot: Implement a bit spinlock to protect the realmode stack
From: Thomas Gleixner <tglx@...utronix.de>
[ Upstream commit f6f1ae9128d2a080ecdd55f85e8a0ca3ed1d58eb ]
Parallel AP bringup requires that the APs can run fully parallel through
the early startup code including the real mode trampoline.
To prepare for this implement a bit-spinlock to serialize access to the
real mode stack so that parallel upcoming APs are not going to corrupt each
others stack while going through the real mode startup code.
Co-developed-by: David Woodhouse <dwmw@...zon.co.uk>
Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Michael Kelley <mikelley@...rosoft.com>
Tested-by: Oleksandr Natalenko <oleksandr@...alenko.name>
Tested-by: Helge Deller <deller@....de> # parisc
Tested-by: Guilherme G. Piccoli <gpiccoli@...lia.com> # Steam Deck
Link: https://lore.kernel.org/r/20230512205257.355425551@linutronix.de
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
arch/x86/include/asm/realmode.h | 3 +++
arch/x86/kernel/head_64.S | 12 ++++++++++++
arch/x86/realmode/init.c | 3 +++
arch/x86/realmode/rm/trampoline_64.S | 23 ++++++++++++++++++-----
4 files changed, 36 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
index f6a1737c77be2..87e5482acd0dc 100644
--- a/arch/x86/include/asm/realmode.h
+++ b/arch/x86/include/asm/realmode.h
@@ -52,6 +52,7 @@ struct trampoline_header {
u64 efer;
u32 cr4;
u32 flags;
+ u32 lock;
#endif
};
@@ -64,6 +65,8 @@ extern unsigned long initial_stack;
extern unsigned long initial_vc_handler;
#endif
+extern u32 *trampoline_lock;
+
extern unsigned char real_mode_blob[];
extern unsigned char real_mode_relocs[];
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 113c13376e512..6acf013c3a2c8 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -251,6 +251,16 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
movq pcpu_hot + X86_current_task(%rdx), %rax
movq TASK_threadsp(%rax), %rsp
+ /*
+ * Now that this CPU is running on its own stack, drop the realmode
+ * protection. For the boot CPU the pointer is NULL!
+ */
+ movq trampoline_lock(%rip), %rax
+ testq %rax, %rax
+ jz .Lsetup_gdt
+ movl $0, (%rax)
+
+.Lsetup_gdt:
/*
* We must switch to a new descriptor in kernel space for the GDT
* because soon the kernel won't have access anymore to the userspace
@@ -433,6 +443,8 @@ SYM_DATA(initial_code, .quad x86_64_start_kernel)
#ifdef CONFIG_AMD_MEM_ENCRYPT
SYM_DATA(initial_vc_handler, .quad handle_vc_boot_ghcb)
#endif
+
+SYM_DATA(trampoline_lock, .quad 0);
__FINITDATA
__INIT
diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index af565816d2ba6..788e5559549f3 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -154,6 +154,9 @@ static void __init setup_real_mode(void)
trampoline_header->flags = 0;
+ trampoline_lock = &trampoline_header->lock;
+ *trampoline_lock = 0;
+
trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd);
/* Map the real mode stub as virtual == physical */
diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
index e38d61d6562e4..4822ad2a5e898 100644
--- a/arch/x86/realmode/rm/trampoline_64.S
+++ b/arch/x86/realmode/rm/trampoline_64.S
@@ -37,6 +37,20 @@
.text
.code16
+.macro LOAD_REALMODE_ESP
+ /*
+ * Make sure only one CPU fiddles with the realmode stack
+ */
+.Llock_rm\@:
+ lock btsl $0, tr_lock
+ jnc 2f
+ pause
+ jmp .Llock_rm\@
+2:
+ # Setup stack
+ movl $rm_stack_end, %esp
+.endm
+
.balign PAGE_SIZE
SYM_CODE_START(trampoline_start)
cli # We should be safe anyway
@@ -49,8 +63,7 @@ SYM_CODE_START(trampoline_start)
mov %ax, %es
mov %ax, %ss
- # Setup stack
- movl $rm_stack_end, %esp
+ LOAD_REALMODE_ESP
call verify_cpu # Verify the cpu supports long mode
testl %eax, %eax # Check for return code
@@ -93,8 +106,7 @@ SYM_CODE_START(sev_es_trampoline_start)
mov %ax, %es
mov %ax, %ss
- # Setup stack
- movl $rm_stack_end, %esp
+ LOAD_REALMODE_ESP
jmp .Lswitch_to_protected
SYM_CODE_END(sev_es_trampoline_start)
@@ -177,7 +189,7 @@ SYM_CODE_START(pa_trampoline_compat)
* In compatibility mode. Prep ESP and DX for startup_32, then disable
* paging and complete the switch to legacy 32-bit mode.
*/
- movl $rm_stack_end, %esp
+ LOAD_REALMODE_ESP
movw $__KERNEL_DS, %dx
movl $(CR0_STATE & ~X86_CR0_PG), %eax
@@ -241,6 +253,7 @@ SYM_DATA_START(trampoline_header)
SYM_DATA(tr_efer, .space 8)
SYM_DATA(tr_cr4, .space 4)
SYM_DATA(tr_flags, .space 4)
+ SYM_DATA(tr_lock, .space 4)
SYM_DATA_END(trampoline_header)
#include "trampoline_common.S"
--
2.39.2
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