Re: [PATCH] calibrate_tsc(): use the Stall() EFI boot service on GRUB_MACHINE_EFI

[Laszlo Ersek <lersek@redhat.com>]

On 11/26/14 14:42, Andrei Borzenkov wrote:
> On Wed, Nov 26, 2014 at 11:59 AM, Laszlo Ersek <lersek@redhat.com> wrote:
>> HyperV Gen2 virtual machines have no PIT; guest code should rely on UEFI
>> services instead.
>>
> 
> Your patch affects all EFI systems;

Which is intended -- No UEFI system guarantees the presence of the PIT,
but they are all required to provide the gBS->Stall() boot service.

So, the current PIT-based code may or may not work on a random UEFI
system (and in fact it happens to fail in HyperV Gen2 guests, because
those actually exploit the no-legacy liberty provided by the UEFI spec),
but the proposed replacement (== rely on gBS->Stall()) *must* work on
all UEFI systems.

For example, the patch works on top of OVMF in a QEMU/KVM guest too (==
different UEFI firmware implementation and different hypervisor).

> is it possible to detect HyperV at
> this level?

Perhaps, but that should definitely not be done. Enlightenment is not
the way to go about this.

Thanks
Laszlo

>> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1150698
>> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1160128
>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>> ---
>>
>> Notes:
>>     Please note that I'm not subscribed to the list.
>>
>>  grub-core/kern/i386/tsc.c | 20 ++++++++++++++++----
>>  1 file changed, 16 insertions(+), 4 deletions(-)
>>
>> diff --git a/grub-core/kern/i386/tsc.c b/grub-core/kern/i386/tsc.c
>> index 3a4cae6..e499648 100644
>> --- a/grub-core/kern/i386/tsc.c
>> +++ b/grub-core/kern/i386/tsc.c
>> @@ -26,9 +26,14 @@
>>  #include <grub/i386/tsc.h>
>>  #include <grub/i386/cpuid.h>
>>  #ifdef GRUB_MACHINE_XEN
>> -#include <grub/xen.h>
>> +# include <grub/xen.h>
>>  #else
>> -#include <grub/i386/pit.h>
>> +# ifdef GRUB_MACHINE_EFI
>> +#  include <grub/efi/efi.h>
>> +#  include <grub/efi/api.h>
>> +# else
>> +#  include <grub/i386/pit.h>
>> +# endif
>>  #endif
>>  #include <grub/cpu/io.h>
>>
>> @@ -72,8 +77,14 @@ grub_cpu_is_tsc_supported (void)
>>  #ifndef GRUB_MACHINE_XEN
>>
>>  static void
>> -grub_pit_wait (grub_uint16_t tics)
>> +grub_stall (grub_uint16_t tics)
>>  {
>> +# ifdef GRUB_MACHINE_EFI
>> +  grub_uint64_t microseconds;
>> +
>> +  microseconds = (grub_uint64_t)tics * 1000 * 1000 * 3 / 3579545;
>> +  efi_call_1 (grub_efi_system_table->boot_services->stall, microseconds);
>> +# else
>>    /* Disable timer2 gate and speaker.  */
>>    grub_outb (grub_inb (GRUB_PIT_SPEAKER_PORT)
>>              & ~ (GRUB_PIT_SPK_DATA | GRUB_PIT_SPK_TMR2),
>> @@ -97,6 +108,7 @@ grub_pit_wait (grub_uint16_t tics)
>>    grub_outb (grub_inb (GRUB_PIT_SPEAKER_PORT)
>>              & ~ (GRUB_PIT_SPK_DATA | GRUB_PIT_SPK_TMR2),
>>               GRUB_PIT_SPEAKER_PORT);
>> +# endif
>>  }
>>  #endif
>>
>> @@ -119,7 +131,7 @@ calibrate_tsc (void)
>>    grub_uint64_t end_tsc;
>>
>>    tsc_boot_time = grub_get_tsc ();
>> -  grub_pit_wait (0xffff);
>> +  grub_stall (0xffff);
>>    end_tsc = grub_get_tsc ();
>>
>>    grub_tsc_rate = grub_divmod64 ((55ULL << 32), end_tsc - tsc_boot_time, 0);
>> --
>> 1.8.3.1
>>
>>
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