File 5a4fd894-4-clarifications-to-wait-infrastructure.patch of Package xen
# Commit 2d1c82261d966735e82e5971eddb63ba3c565a37
# Date 2018-01-05 19:57:08 +0000
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
common/wait: Clarifications to wait infrastructure
This logic is not as clear as it could be. Add some comments to help.
Rearrange the asm block in __prepare_to_wait() to separate the GPR
saving/restoring from the internal logic.
While tweaking, add an unreachable() following the jmp in
check_wakeup_from_wait().
No functional change.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
--- a/xen/common/wait.c
+++ b/xen/common/wait.c
@@ -138,14 +138,26 @@ static void __prepare_to_wait(struct wai
domain_crash_synchronous();
}
+ /* Hand-rolled setjmp(). */
asm volatile (
- "push %%rax; push %%rbx; push %%rdx; "
- "push %%rbp; push %%r8; push %%r9; push %%r10; push %%r11; "
- "push %%r12; push %%r13; push %%r14; push %%r15; call 1f; "
- "1: addq $2f-1b,(%%rsp); sub %%esp,%%ecx; cmp %3,%%ecx; ja 3f; "
- "mov %%rsp,%%rsi; 2: rep movsb; mov %%rsp,%%rsi; 3: pop %%rax; "
- "pop %%r15; pop %%r14; pop %%r13; pop %%r12; "
- "pop %%r11; pop %%r10; pop %%r9; pop %%r8; "
+ "push %%rax; push %%rbx; push %%rdx; push %%rbp;"
+ "push %%r8; push %%r9; push %%r10; push %%r11;"
+ "push %%r12; push %%r13; push %%r14; push %%r15;"
+
+ "call 1f;"
+ "1: addq $2f-1b,(%%rsp);"
+ "sub %%esp,%%ecx;"
+ "cmp %3,%%ecx;"
+ "ja 3f;"
+ "mov %%rsp,%%rsi;"
+
+ /* check_wakeup_from_wait() longjmp()'s to this point. */
+ "2: rep movsb;"
+ "mov %%rsp,%%rsi;"
+ "3: pop %%rax;"
+
+ "pop %%r15; pop %%r14; pop %%r13; pop %%r12;"
+ "pop %%r11; pop %%r10; pop %%r9; pop %%r8;"
"pop %%rbp; pop %%rdx; pop %%rbx; pop %%rax"
: "=&S" (wqv->esp), "=&c" (dummy), "=&D" (dummy)
: "i" (PAGE_SIZE), "0" (0), "1" (cpu_info), "2" (wqv->stack)
@@ -189,11 +201,16 @@ void check_wakeup_from_wait(void)
wait(); /* takes us back into the scheduler */
}
+ /*
+ * Hand-rolled longjmp(). Returns to the pointer on the top of
+ * wqv->stack, and lands on a `rep movs` instruction.
+ */
asm volatile (
"mov %1,%%"__OP"sp; jmp *(%0)"
: : "S" (wqv->stack), "D" (wqv->esp),
"c" ((char *)get_cpu_info() - (char *)wqv->esp)
: "memory" );
+ unreachable();
}
#else /* !CONFIG_X86 */