x86/io: Speedup schedule out of I/O bitmap user

There is no requirement to update the TSS I/O bitmap when a thread using it is
scheduled out and the incoming thread does not use it.

For the permission check based on the TSS I/O bitmap the CPU calculates the memory
location of the I/O bitmap by the address of the TSS and the io_bitmap_base member
of the tss_struct. The easiest way to invalidate the I/O bitmap is to switch the
offset to an address outside of the TSS limit.

If an I/O instruction is issued from user space the TSS limit causes #GP to be
raised in the same was as valid I/O bitmap with all bits set to 1 would do.

This removes the extra work when an I/O bitmap using task is scheduled out
and puts the burden on the rare I/O bitmap users when they are scheduled
in.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 6e0a3b4..6d0059c 100644 (file)
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -330,8 +330,23 @@ struct x86_hw_tss {
 #define IO_BITMAP_BITS                 65536
 #define IO_BITMAP_BYTES                        (IO_BITMAP_BITS/8)
 #define IO_BITMAP_LONGS                        (IO_BITMAP_BYTES/sizeof(long))
-#define IO_BITMAP_OFFSET               (offsetof(struct tss_struct, io_bitmap) - offsetof(struct tss_struct, x86_tss))
-#define INVALID_IO_BITMAP_OFFSET       0x8000
+
+#define IO_BITMAP_OFFSET_VALID                         \
+       (offsetof(struct tss_struct, io_bitmap) -       \
+        offsetof(struct tss_struct, x86_tss))
+
+/*
+ * sizeof(unsigned long) coming from an extra "long" at the end
+ * of the iobitmap.
+ *
+ * -1? seg base+limit should be pointing to the address of the
+ * last valid byte
+ */
+#define __KERNEL_TSS_LIMIT     \
+       (IO_BITMAP_OFFSET_VALID + IO_BITMAP_BYTES + sizeof(unsigned long) - 1)
+
+/* Base offset outside of TSS_LIMIT so unpriviledged IO causes #GP */
+#define IO_BITMAP_OFFSET_INVALID       (__KERNEL_TSS_LIMIT + 1)
 
 struct entry_stack {
        unsigned long           words[64];
@@ -349,6 +364,15 @@ struct tss_struct {
         */
        struct x86_hw_tss       x86_tss;
 
+       /*
+        * Store the dirty size of the last io bitmap offender. The next
+        * one will have to do the cleanup as the switch out to a non io
+        * bitmap user will just set x86_tss.io_bitmap_base to a value
+        * outside of the TSS limit. So for sane tasks there is no need to
+        * actually touch the io_bitmap at all.
+        */
+       unsigned int            io_bitmap_prev_max;
+
        /*
         * The extra 1 is there because the CPU will access an
         * additional byte beyond the end of the IO permission
@@ -360,16 +384,6 @@ struct tss_struct {
 
 DECLARE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss_rw);
 
-/*
- * sizeof(unsigned long) coming from an extra "long" at the end
- * of the iobitmap.
- *
- * -1? seg base+limit should be pointing to the address of the
- * last valid byte
- */
-#define __KERNEL_TSS_LIMIT     \
-       (IO_BITMAP_OFFSET + IO_BITMAP_BYTES + sizeof(unsigned long) - 1)
-
 /* Per CPU interrupt stacks */
 struct irq_stack {
        char            stack[IRQ_STACK_SIZE];

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d52ec1a..8c1000a 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1860,7 +1860,8 @@ void cpu_init(void)
 
        /* Initialize the TSS. */
        tss_setup_ist(tss);
-       tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET;
+       tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_INVALID;
+       tss->io_bitmap_prev_max = 0;
        memset(tss->io_bitmap, 0xff, sizeof(tss->io_bitmap));
        set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
 

diff --git a/arch/x86/kernel/doublefault.c b/arch/x86/kernel/doublefault.c
index 0b8cedb..cedb07d 100644 (file)
--- a/arch/x86/kernel/doublefault.c
+++ b/arch/x86/kernel/doublefault.c
@@ -54,7 +54,7 @@ struct x86_hw_tss doublefault_tss __cacheline_aligned = {
        .sp0            = STACK_START,
        .ss0            = __KERNEL_DS,
        .ldt            = 0,
-       .io_bitmap_base = INVALID_IO_BITMAP_OFFSET,
+       .io_bitmap_base = IO_BITMAP_OFFSET_INVALID,
 
        .ip             = (unsigned long) doublefault_fn,
        /* 0x2 bit is always set */

diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index 80fa36b..eed218a 100644 (file)
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -82,6 +82,10 @@ long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
        /* Update the TSS */
        tss = this_cpu_ptr(&cpu_tss_rw);
        memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
+       /* Store the new end of the zero bits */
+       tss->io_bitmap_prev_max = bytes;
+       /* Make the bitmap base in the TSS valid */
+       tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID;
        /* Make sure the TSS limit covers the I/O bitmap. */
        refresh_tss_limit();
 

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7e07f0b..2444fe2 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -72,18 +72,9 @@ __visible DEFINE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss_rw) = {
 #ifdef CONFIG_X86_32
                .ss0 = __KERNEL_DS,
                .ss1 = __KERNEL_CS,
-               .io_bitmap_base = INVALID_IO_BITMAP_OFFSET,
 #endif
+               .io_bitmap_base = IO_BITMAP_OFFSET_INVALID,
         },
-#ifdef CONFIG_X86_32
-        /*
-         * Note that the .io_bitmap member must be extra-big. This is because
-         * the CPU will access an additional byte beyond the end of the IO
-         * permission bitmap. The extra byte must be all 1 bits, and must
-         * be within the limit.
-         */
-       .io_bitmap              = { [0 ... IO_BITMAP_LONGS] = ~0 },
-#endif
 };
 EXPORT_PER_CPU_SYMBOL(cpu_tss_rw);
 
@@ -112,18 +103,18 @@ void exit_thread(struct task_struct *tsk)
        struct thread_struct *t = &tsk->thread;
        unsigned long *bp = t->io_bitmap_ptr;
        struct fpu *fpu = &t->fpu;
+       struct tss_struct *tss;
 
        if (bp) {
-               struct tss_struct *tss = &per_cpu(cpu_tss_rw, get_cpu());
+               preempt_disable();
+               tss = this_cpu_ptr(&cpu_tss_rw);
 
                t->io_bitmap_ptr = NULL;
-               clear_thread_flag(TIF_IO_BITMAP);
-               /*
-                * Careful, clear this in the TSS too:
-                */
-               memset(tss->io_bitmap, 0xff, t->io_bitmap_max);
                t->io_bitmap_max = 0;
-               put_cpu();
+               clear_thread_flag(TIF_IO_BITMAP);
+               /* Invalidate the io bitmap base in the TSS */
+               tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_INVALID;
+               preempt_enable();
                kfree(bp);
        }
 
@@ -369,29 +360,47 @@ void arch_setup_new_exec(void)
        }
 }
 
-static inline void switch_to_bitmap(struct thread_struct *prev,
-                                   struct thread_struct *next,
+static inline void switch_to_bitmap(struct thread_struct *next,
                                    unsigned long tifp, unsigned long tifn)
 {
        struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
 
        if (tifn & _TIF_IO_BITMAP) {
                /*
-                * Copy the relevant range of the IO bitmap.
-                * Normally this is 128 bytes or less:
+                * Copy at least the size of the incoming tasks bitmap
+                * which covers the last permitted I/O port.
+                *
+                * If the previous task which used an io bitmap had more
+                * bits permitted, then the copy needs to cover those as
+                * well so they get turned off.
                 */
                memcpy(tss->io_bitmap, next->io_bitmap_ptr,
-                      max(prev->io_bitmap_max, next->io_bitmap_max));
+                      max(tss->io_bitmap_prev_max, next->io_bitmap_max));
+
+               /* Store the new max and set io_bitmap_base valid */
+               tss->io_bitmap_prev_max = next->io_bitmap_max;
+               tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID;
+
                /*
-                * Make sure that the TSS limit is correct for the CPU
-                * to notice the IO bitmap.
+                * Make sure that the TSS limit is covering the io bitmap.
+                * It might have been cut down by a VMEXIT to 0x67 which
+                * would cause a subsequent I/O access from user space to
+                * trigger a #GP because tbe bitmap is outside the TSS
+                * limit.
                 */
                refresh_tss_limit();
        } else if (tifp & _TIF_IO_BITMAP) {
                /*
-                * Clear any possible leftover bits:
+                * Do not touch the bitmap. Let the next bitmap using task
+                * deal with the mess. Just make the io_bitmap_base invalid
+                * by moving it outside the TSS limit so any subsequent I/O
+                * access from user space will trigger a #GP.
+                *
+                * This is correct even when VMEXIT rewrites the TSS limit
+                * to 0x67 as the only requirement is that the base points
+                * outside the limit.
                 */
-               memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
+               tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_INVALID;
        }
 }
 
@@ -605,7 +614,7 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p)
 
        tifn = READ_ONCE(task_thread_info(next_p)->flags);
        tifp = READ_ONCE(task_thread_info(prev_p)->flags);
-       switch_to_bitmap(prev, next, tifp, tifn);
+       switch_to_bitmap(next, tifp, tifn);
 
        propagate_user_return_notify(prev_p, next_p);