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Subject[RFC 20/30] x86/entry: Add C code for fast system call entries
Date
This handles both SYSENTER and SYSCALL.  The asm glue will take care
of the differences.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/entry/common.c | 39 +++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 41d17508cf46..5725cdcec4de 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -24,6 +24,8 @@

#include <asm/desc.h>
#include <asm/traps.h>
+#include <asm/vdso.h>
+#include <asm/uaccess.h>

#define CREATE_TRACE_POINTS
#include <trace/events/syscalls.h>
@@ -360,4 +362,41 @@ __visible void do_int80_syscall_32(struct pt_regs *regs)

syscall_return_slowpath(regs);
}
+
+__visible void do_fast_syscall_32(struct pt_regs *regs)
+{
+ /*
+ * Called using the internal vDSO SYSENTER calling convention.
+ * Adjust regs so it looks like we entered using int80.
+ */
+
+ unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
+ vdso_image_32.sym_int80_landing_pad;
+
+ /* SYSENTER loses EIP. Fix it up. */
+ regs->ip = landing_pad;
+
+ /*
+ * Fetch ECX from where the vDSO stashed it.
+ *
+ * WARNING: We are in CONTEXT_USER and RCU isn't paying attention!
+ */
+ local_irq_enable();
+ if (get_user(*(u32 *)&regs->cx,
+ (u32 __user __force *)(unsigned long)(u32)regs->sp)) {
+ /* User code screwed up. */
+ local_irq_disable();
+ regs->ax = -EFAULT;
+#ifdef CONFIG_CONTEXT_TRACKING
+ enter_from_user_mode();
+#endif
+ prepare_exit_to_usermode(regs);
+ return;
+ }
+ local_irq_disable();
+
+ /* Now this is just like a normal syscall. */
+ do_int80_syscall_32(regs);
+ return;
+}
#endif
--
2.4.3


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