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Subject[PATCH V6 46/49] x86/entry: Remove ASM function paranoid_entry() and paranoid_exit()
Date
From: Lai Jiangshan <laijs@linux.alibaba.com>

IST exceptions are changed to use C entry code which uses the C function
ist_paranoid_entry() and ist_paranoid_exit(). The ASM function
paranoid_entry() and paranoid_exit() are useless.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/entry/entry_64.S | 126 --------------------------------------
1 file changed, 126 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 614e6cbb871b..a583089e88c1 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -848,132 +848,6 @@ SYM_CODE_START(xen_failsafe_callback)
SYM_CODE_END(xen_failsafe_callback)
#endif /* CONFIG_XEN_PV */

-/*
- * Save all registers in pt_regs. Return GSBASE related information
- * in EBX depending on the availability of the FSGSBASE instructions:
- *
- * FSGSBASE R/EBX
- * N 0 -> SWAPGS on exit
- * 1 -> no SWAPGS on exit
- *
- * Y GSBASE value at entry, must be restored in paranoid_exit
- */
-SYM_CODE_START_LOCAL(paranoid_entry)
- UNWIND_HINT_FUNC
-
- /*
- * Always stash CR3 in %r14. This value will be restored,
- * verbatim, at exit. Needed if paranoid_entry interrupted
- * another entry that already switched to the user CR3 value
- * but has not yet returned to userspace.
- *
- * This is also why CS (stashed in the "iret frame" by the
- * hardware at entry) can not be used: this may be a return
- * to kernel code, but with a user CR3 value.
- *
- * Switching CR3 does not depend on kernel GSBASE so it can
- * be done before switching to the kernel GSBASE. This is
- * required for FSGSBASE because the kernel GSBASE has to
- * be retrieved from a kernel internal table.
- */
- SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14
-
- /*
- * Handling GSBASE depends on the availability of FSGSBASE.
- *
- * Without FSGSBASE the kernel enforces that negative GSBASE
- * values indicate kernel GSBASE. With FSGSBASE no assumptions
- * can be made about the GSBASE value when entering from user
- * space.
- */
- ALTERNATIVE "jmp .Lparanoid_entry_checkgs", "", X86_FEATURE_FSGSBASE
-
- /*
- * Read the current GSBASE and store it in %rbx unconditionally,
- * retrieve and set the current CPUs kernel GSBASE. The stored value
- * has to be restored in paranoid_exit unconditionally.
- *
- * The unconditional write to GS base below ensures that no subsequent
- * loads based on a mispredicted GS base can happen, therefore no LFENCE
- * is needed here.
- */
- SAVE_AND_SET_GSBASE scratch_reg=%rax save_reg=%rbx
- ret
-
-.Lparanoid_entry_checkgs:
- /* EBX = 1 -> kernel GSBASE active, no restore required */
- movl $1, %ebx
- /*
- * The kernel-enforced convention is a negative GSBASE indicates
- * a kernel value. No SWAPGS needed on entry and exit.
- */
- movl $MSR_GS_BASE, %ecx
- rdmsr
- testl %edx, %edx
- js .Lparanoid_kernel_gsbase
-
- /* EBX = 0 -> SWAPGS required on exit */
- xorl %ebx, %ebx
- swapgs
-.Lparanoid_kernel_gsbase:
-
- /*
- * The above SAVE_AND_SWITCH_TO_KERNEL_CR3 macro doesn't do an
- * unconditional CR3 write, even in the PTI case. So do an lfence
- * to prevent GS speculation, regardless of whether PTI is enabled.
- */
- FENCE_SWAPGS_KERNEL_ENTRY
- ret
-SYM_CODE_END(paranoid_entry)
-
-/*
- * "Paranoid" exit path from exception stack. This is invoked
- * only on return from IST interrupts that came from kernel space.
- *
- * We may be returning to very strange contexts (e.g. very early
- * in syscall entry), so checking for preemption here would
- * be complicated. Fortunately, there's no good reason to try
- * to handle preemption here.
- *
- * R/EBX contains the GSBASE related information depending on the
- * availability of the FSGSBASE instructions:
- *
- * FSGSBASE R/EBX
- * N 0 -> SWAPGS on exit
- * 1 -> no SWAPGS on exit
- *
- * Y User space GSBASE, must be restored unconditionally
- */
-SYM_CODE_START_LOCAL(paranoid_exit)
- UNWIND_HINT_REGS offset=8
- /*
- * The order of operations is important. RESTORE_CR3 requires
- * kernel GSBASE.
- *
- * NB to anyone to try to optimize this code: this code does
- * not execute at all for exceptions from user mode. Those
- * exceptions go through error_exit instead.
- */
- RESTORE_CR3 scratch_reg=%rax save_reg=%r14
-
- /* Handle the three GSBASE cases */
- ALTERNATIVE "jmp .Lparanoid_exit_checkgs", "", X86_FEATURE_FSGSBASE
-
- /* With FSGSBASE enabled, unconditionally restore GSBASE */
- wrgsbase %rbx
- ret
-
-.Lparanoid_exit_checkgs:
- /* On non-FSGSBASE systems, conditionally do SWAPGS */
- testl %ebx, %ebx
- jnz .Lparanoid_exit_done
-
- /* We are returning to a context with user GSBASE */
- swapgs
-.Lparanoid_exit_done:
- ret
-SYM_CODE_END(paranoid_exit)
-
SYM_CODE_START_LOCAL(error_return)
UNWIND_HINT_REGS
DEBUG_ENTRY_ASSERT_IRQS_OFF
--
2.19.1.6.gb485710b
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