[Xen-devel] Re: question about patch 13252

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> "Lu, Guanqun" <guanqun.lu@xxxxxxxxx> 19.03.09 15:07 >>>
>I saw that in patch 13252,
>you added such lines in xen/arch/x86/traps.c
>
>+#ifdef CONFIG_COMPAT
>+    _set_tssldt_desc(
>+        compat_gdt_table + __TSS(n) - FIRST_RESERVED_GDT_ENTRY,
>+        (unsigned long)addr,
>+        offsetof(struct tss_struct, __cacheline_filler) - 1,
>+        11);
>+#endif
>
>I have such question about the number 11, 11 is 1010 in binary format,
>which means that the busy flat is set.  Then later, load_TR() is called.
>load_TR() is a wrapper around instruction 'ltr'.  As I consult SDM2A,
>it says that ltr will generate #GP, when the busy flag is set.
>
>So I'm a little puzzled. Can you explain a little why it's not 9 ?
>Or am I missing something here?

You're not running on compat_gdt_table when doing the ltr, and when
you switch between GDTs the busy bits must be in sync.

Jan


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