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x86/fpu, lguest: Remove CR0.TS support

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Now that Linux never sets CR0.TS, lguest doesn't need to support it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kvm list <kvm@vger.kernel.org>
Link: http://lkml.kernel.org/r/8a7bf2c11231c082258fd67705d0f275639b8475.1477951965.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski
2016-10-31 15:18:46 -07:00
committed by Ingo Molnar
parent 04ac88abaf
commit cd95ea81f2
5 changed files with 8 additions and 34 deletions
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17
arch/x86/lguest/boot.c
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@@ -497,27 +497,24 @@ static void lguest_cpuid(unsigned int *ax, unsigned int *bx,
* a whole series of functions like read_cr0() and write_cr0().
*
* We start with cr0. cr0 allows you to turn on and off all kinds of basic
* features, but Linux only really cares about one: the horrifically-named Task
* Switched (TS) bit at bit 3 (ie. 8)
* features, but the only cr0 bit that Linux ever used at runtime was the
* horrifically-named Task Switched (TS) bit at bit 3 (ie. 8)
*
* What does the TS bit do? Well, it causes the CPU to trap (interrupt 7) if
* the floating point unit is used. Which allows us to restore FPU state
* lazily after a task switch, and Linux uses that gratefully, but wouldn't a
* name like "FPUTRAP bit" be a little less cryptic?
* lazily after a task switch if we wanted to, but wouldn't a name like
* "FPUTRAP bit" be a little less cryptic?
*
* We store cr0 locally because the Host never changes it. The Guest sometimes
* wants to read it and we'd prefer not to bother the Host unnecessarily.
* Fortunately, Linux keeps it simple and doesn't use TS, so we can ignore
* cr0.
*/
static unsigned long current_cr0;
static void lguest_write_cr0(unsigned long val)
{
lazy_hcall1(LHCALL_TS, val & X86_CR0_TS);
current_cr0 = val;
}
static unsigned long lguest_read_cr0(void)
{
return current_cr0;
return 0;
}
/*