[Xen-devel] [PATCH RFC 42/44] x86/smp: Allocate a percpu linear range for the TSS

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

With all CPUs using the same virtual stack mapping, the TSS rsp0/ist[0..2]
values are compile-time constant.  Therefore, we can use a single read-only
TSS for the whole system.

To faciliate this, a new .rodata.page_aligned section needs introducing.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/smpboot.c          |  6 ++++++
 xen/arch/x86/traps.c            | 29 +++++++++++++++++++++++++++++
 xen/arch/x86/xen.lds.S          |  2 ++
 xen/include/asm-x86/config.h    |  1 +
 xen/include/asm-x86/processor.h |  2 ++
 5 files changed, 40 insertions(+)

diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 77ee883..fa99e4d 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -800,6 +800,12 @@ static int cpu_smpboot_alloc_common(unsigned int cpu)
     if ( rc )
         goto out;
 
+    /* Map the TSS. */
+    rc = percpu_map_frame(cpu, PERCPU_TSS_MAPPING,
+                          virt_to_page(&global_tss), PAGE_HYPERVISOR_RO);
+    if ( rc )
+        goto out;
+
     /* Allocate space for the mapcache L1e's... */
     rc = percpu_alloc_l1t(cpu, PERCPU_MAPCACHE_START, &pg);
     if ( rc )
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 493f8f3..0ab10ba 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -108,6 +108,35 @@ __section(".bss.page_aligned") __aligned(PAGE_SIZE);
 /* Pointer to the IDT of every CPU. */
 idt_entry_t *idt_tables[NR_CPUS] __read_mostly;
 
+/* Global TSS.  All stack entry points are identical on each CPU. */
+const struct tss_struct global_tss
+__section(".rodata.page_aligned") __aligned(PAGE_SIZE) =
+{
+    /* Main stack for interrupts/exceptions. */
+    .rsp0 = (PERCPU_STACK_MAPPING + STACK_SIZE -
+             sizeof(struct cpu_info) +
+             offsetof(struct cpu_info, guest_cpu_user_regs.es)) ,
+
+    /* Ring 1 and 2 stacks poisoned. */
+    .rsp1 = 0x8600111111111111ul,
+    .rsp2 = 0x8600111111111111ul,
+
+    /*
+     * MCE, NMI and Double Fault handlers get their own stacks.
+     * All others poisoned.
+     */
+    .ist = {
+        [IST_MCE - 1] = PERCPU_STACK_MAPPING + IST_MCE * PAGE_SIZE,
+        [IST_DF  - 1] = PERCPU_STACK_MAPPING + IST_DF  * PAGE_SIZE,
+        [IST_NMI - 1] = PERCPU_STACK_MAPPING + IST_NMI * PAGE_SIZE,
+
+        [IST_MAX ... ARRAY_SIZE(global_tss.ist) - 1] =
+            0x8600111111111111ul,
+    },
+
+    .bitmap = IOBMP_INVALID_OFFSET,
+};
+
 void (*ioemul_handle_quirk)(
     u8 opcode, char *io_emul_stub, struct cpu_user_regs *regs);
 
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index d5e8821..3456b4c 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -77,6 +77,8 @@ SECTIONS
   __2M_rodata_start = .;       /* Start of 2M superpages, mapped RO. */
   .rodata : {
        _srodata = .;
+       *(.rodata.page_aligned)
+       . = ALIGN(PAGE_SIZE);
        /* Bug frames table */
        __start_bug_frames = .;
        *(.bug_frames.0)
diff --git a/xen/include/asm-x86/config.h b/xen/include/asm-x86/config.h
index 3974748..caff09f 100644
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -283,6 +283,7 @@ extern unsigned long xen_phys_start;
 
 /* Mappings in the percpu area: */
 #define PERCPU_IDT_MAPPING       (PERCPU_LINEAR_START + KB(4))
+#define PERCPU_TSS_MAPPING       (PERCPU_LINEAR_START + KB(128))
 
 #define PERCPU_MAPCACHE_L1ES     (PERCPU_LINEAR_START + MB(2) + KB(12))
 #define PERCPU_MAPCACHE_START    (PERCPU_LINEAR_START + MB(4))
diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
index c206080..22882a6 100644
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -475,6 +475,8 @@ static inline void disable_each_ist(idt_entry_t *idt)
 extern idt_entry_t idt_table[];
 extern idt_entry_t *idt_tables[];
 
+extern const struct tss_struct global_tss;
+
 DECLARE_PER_CPU(struct tss_struct, init_tss);
 
 extern void init_int80_direct_trap(struct vcpu *v);
-- 
2.1.4


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