x86/boot: Port I/O: Allow to hook up alternative helpers

Port I/O instructions trigger #VE in the TDX environment. In response to
the exception, kernel emulates these instructions using hypercalls.

But during early boot, on the decompression stage, it is cumbersome to
deal with #VE. It is cleaner to go to hypercalls directly, bypassing #VE
handling.

Add a way to hook up alternative port I/O helpers in the boot stub with
a new pio_ops structure.  For now, set the ops structure to just call
the normal I/O operation functions.

out*()/in*() macros redefined to use pio_ops callbacks. It eliminates
need in changing call sites. io_delay() changed to use port I/O helper
instead of inline assembly.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20220405232939.73860-16-kirill.shutemov@linux.intel.com

diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index 22a474c..b42b916 100644 (file)
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -23,10 +23,10 @@
 #include <linux/edd.h>
 #include <asm/setup.h>
 #include <asm/asm.h>
-#include <asm/shared/io.h>
 #include "bitops.h"
 #include "ctype.h"
 #include "cpuflags.h"
+#include "io.h"
 
 /* Useful macros */
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof(*(x)))
@@ -39,7 +39,7 @@ extern struct boot_params boot_params;
 static inline void io_delay(void)
 {
        const u16 DELAY_PORT = 0x80;
-       asm volatile("outb %%al,%0" : : "dN" (DELAY_PORT));
+       outb(0, DELAY_PORT);
 }
 
 /* These functions are used to reference data in other segments. */

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index e8142e9..fa8969f 100644 (file)
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -48,6 +48,8 @@ void *memmove(void *dest, const void *src, size_t n);
  */
 struct boot_params *boot_params;
 
+struct port_io_ops pio_ops;
+
 memptr free_mem_ptr;
 memptr free_mem_end_ptr;
 
@@ -371,6 +373,8 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
        lines = boot_params->screen_info.orig_video_lines;
        cols = boot_params->screen_info.orig_video_cols;
 
+       init_default_io_ops();
+
        /*
         * Detect TDX guest environment.
         *

diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 8a253e8..ea71cf3 100644 (file)
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -26,7 +26,6 @@
 #include <asm/boot.h>
 #include <asm/bootparam.h>
 #include <asm/desc_defs.h>
-#include <asm/shared/io.h>
 
 #include "tdx.h"
 
@@ -35,6 +34,7 @@
 
 #define BOOT_BOOT_H
 #include "../ctype.h"
+#include "../io.h"
 
 #ifdef CONFIG_X86_64
 #define memptr long

diff --git a/arch/x86/boot/io.h b/arch/x86/boot/io.h
new file mode 100644 (file)
index 0000000..1108809
--- /dev/null
+++ b/arch/x86/boot/io.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef BOOT_IO_H
+#define BOOT_IO_H
+
+#include <asm/shared/io.h>
+
+#undef inb
+#undef inw
+#undef inl
+#undef outb
+#undef outw
+#undef outl
+
+struct port_io_ops {
+       u8      (*f_inb)(u16 port);
+       void    (*f_outb)(u8 v, u16 port);
+       void    (*f_outw)(u16 v, u16 port);
+};
+
+extern struct port_io_ops pio_ops;
+
+/*
+ * Use the normal I/O instructions by default.
+ * TDX guests override these to use hypercalls.
+ */
+static inline void init_default_io_ops(void)
+{
+       pio_ops.f_inb  = __inb;
+       pio_ops.f_outb = __outb;
+       pio_ops.f_outw = __outw;
+}
+
+/*
+ * Redirect port I/O operations via pio_ops callbacks.
+ * TDX guests override these callbacks with TDX-specific helpers.
+ */
+#define inb  pio_ops.f_inb
+#define outb pio_ops.f_outb
+#define outw pio_ops.f_outw
+
+#endif

diff --git a/arch/x86/boot/main.c b/arch/x86/boot/main.c
index e3add85..1202d4f 100644 (file)
--- a/arch/x86/boot/main.c
+++ b/arch/x86/boot/main.c
@@ -17,6 +17,8 @@
 
 struct boot_params boot_params __attribute__((aligned(16)));
 
+struct port_io_ops pio_ops;
+
 char *HEAP = _end;
 char *heap_end = _end;         /* Default end of heap = no heap */
 
@@ -133,6 +135,8 @@ static void init_heap(void)
 
 void main(void)
 {
+       init_default_io_ops();
+
        /* First, copy the boot header into the "zeropage" */
        copy_boot_params();
 

diff --git a/arch/x86/realmode/rm/wakemain.c b/arch/x86/realmode/rm/wakemain.c
index 1d6437e..a6f4d83 100644 (file)
--- a/arch/x86/realmode/rm/wakemain.c
+++ b/arch/x86/realmode/rm/wakemain.c
@@ -62,8 +62,12 @@ static void send_morse(const char *pattern)
        }
 }
 
+struct port_io_ops pio_ops;
+
 void main(void)
 {
+       init_default_io_ops();
+
        /* Kill machine if structures are wrong */
        if (wakeup_header.real_magic != 0x12345678)
                while (1)