Re: [Qemu-devel] [PATCH v10 3/6] tpm: allocate/map buffer for TPM Physical Presence interface

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 03 Sep 2018 23:48:15 +0200
Juan Quintela <quintela@redhat.com> wrote:

> Marc-André Lureau <marcandre.lureau@gmail.com> wrote:
> > Hi
> >
> > On Fri, Aug 31, 2018 at 7:32 PM Marc-André Lureau
> > <marcandre.lureau@redhat.com> wrote:  
> >>
> >> From: Stefan Berger <stefanb@linux.vnet.ibm.com>
> >>
> >> Implement a virtual memory device for the TPM Physical Presence interface.
> >> The memory is located at 0xFED45000 and used by ACPI to send messages to the
> >> firmware (BIOS) and by the firmware to provide parameters for each one of
> >> the supported codes.
> >>
> >> This interface should be used by all TPM devices on x86 and can be
> >> added by calling tpm_ppi_init_io().
> >>
> >> Note: bios_linker cannot be used to allocate the PPI memory region,
> >> since the reserved memory should stay stable across reboots, and might
> >> be needed before the ACPI tables are installed.
> >>
> >> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
> >> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> >> Reviewed-by: Igor Mammedov <imammedo@redhat.com>  
> 
> 
> ....
> 
> >> + */
> >> +#define TPM_PPI_ADDR_SIZE           0x400
> >> +#define TPM_PPI_ADDR_BASE           0xFED45000  
> 
> > There is a (new) issue with the PPI ram region:
> >
> > READ of size 32 at 0x61d000090480 thread T6
> >     #0 0x5622bd8de0f4 in buffer_zero_avx2
> > /home/elmarco/src/qq/util/bufferiszero.c:169
> >     #1 0x5622bd8de899 in select_accel_fn
> > /home/elmarco/src/qq/util/bufferiszero.c:282
> >     #2 0x5622bd8de8f1 in buffer_is_zero
> > /home/elmarco/src/qq/util/bufferiszero.c:309
> >     #3 0x5622bc209f94 in is_zero_range /home/elmarco/src/qq/migration/ram.c:82
> >     #4 0x5622bc21938d in save_zero_page_to_file
> > /home/elmarco/src/qq/migration/ram.c:1694
> >     #5 0x5622bc219452 in save_zero_page
> > /home/elmarco/src/qq/migration/ram.c:1713
> >     #6 0x5622bc21db67 in ram_save_target_page
> > /home/elmarco/src/qq/migration/ram.c:2289
> >     #7 0x5622bc21e13e in ram_save_host_page
> > /home/elmarco/src/qq/migration/ram.c:2351
> >     #8 0x5622bc21ea3a in ram_find_and_save_block
> > /home/elmarco/src/qq/migration/ram.c:2413
> >     #9 0x5622bc223b5d in ram_save_iterate
> > /home/elmarco/src/qq/migration/ram.c:3193
> >     #10 0x5622bd16f544 in qemu_savevm_state_iterate
> > /home/elmarco/src/qq/migration/savevm.c:1103
> >     #11 0x5622bd157e75 in migration_iteration_run
> > /home/elmarco/src/qq/migration/migration.c:2897
> >     #12 0x5622bd15892e in migration_thread
> > /home/elmarco/src/qq/migration/migration.c:3018
> >     #13 0x5622bd902f31 in qemu_thread_start
> > /home/elmarco/src/qq/util/qemu-thread-posix.c:504
> >     #14 0x7f42f0ef4593 in start_thread (/lib64/libpthread.so.0+0x7593)
> >     #15 0x7f42f0c280de in clone (/lib64/libc.so.6+0xfa0de)
> > 0x61d000090490 is located 0 bytes to the right of 2064-byte region
> > [0x61d00008fc80,0x61d000090490)
> >
> > migration code is assuming RAM is multiple of TARGET_PAGE_SIZE.  
> 
> Physical RAM is multiple of TARGET_PAGE_SIZE O:-)
> That assumtion is held in too many places, if you can change the size to
> be multiple of page size, that would be greate.
> 
> > Should the migration code be fixed, or should the TPM code allocate
> > ram differently?  
> 
> Migration people (i.e. me) would preffer that you fix the TPM
> allocation.  Or you can decide that this is *not* RAM.  The unit of
> transfer for migrate ram is ram pages, a.k.a. TARGET_PAGE_SIZE.
I'd loath to waste whole page in already cramped area.
Can we implement it as mmio region? (it will add some bolerplate code for read/write
handlers/migration and cause vmexits on every read/write but it's not a hot path so we might not care)
 
> > In all case, I think the migration code should either be fixed or have
> > an assert.  
> 
> An assert for sure.
> 
> Fixed .... Do we have real devices that put ram regions that are smaller
> than page size?
> 
> Later, Juan.