Re: [PATCH v4 1/2] tpm: CRB: Use ram_device for "tpm-crb-cmd" region

[Eric Auger]

Hi Marc-André,
On 3/3/22 5:16 PM, Marc-André Lureau wrote:
> Hi
> 
> On Thu, Mar 3, 2022 at 6:41 PM Eric Auger <eauger@redhat.com
> <mailto:eauger@redhat.com>> wrote:
> 
>     Hi Stefan,
> 
>     On 2/8/22 6:58 PM, Eric Auger wrote:
>     > Hi Stefan,
>     >
>     > On 2/8/22 6:16 PM, Stefan Berger wrote:
>     >>
>     >> On 2/8/22 08:38, Eric Auger wrote:
>     >>> Representing the CRB cmd/response buffer as a standard
>     >>> RAM region causes some trouble when the device is used
>     >>> with VFIO. Indeed VFIO attempts to DMA_MAP this region
>     >>> as usual RAM but this latter does not have a valid page
>     >>> size alignment causing such an error report:
>     >>> "vfio_listener_region_add received unaligned region".
>     >>> To allow VFIO to detect that failing dma mapping
>     >>> this region is not an issue, let's use a ram_device
>     >>> memory region type instead.
>     >>>
>     >>> Signed-off-by: Eric Auger <eric.auger@redhat.com
>     <mailto:eric.auger@redhat.com>>
>     >>> Tested-by: Stefan Berger <stefanb@linux.ibm.com
>     <mailto:stefanb@linux.ibm.com>>
>     >>> Acked-by: Stefan Berger <stefanb@linux.ibm.com
>     <mailto:stefanb@linux.ibm.com>>
>     >>> [PMD: Keep tpm_crb.c in meson's softmmu_ss]
>     >>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org
>     <mailto:f4bug@amsat.org>>
>     >>
>     >>
>     >> v4 doesn't build for me:
>     >>
>     >> ../hw/tpm/tpm_crb.c: In function ?tpm_crb_realize?:
>     >> ../hw/tpm/tpm_crb.c:297:33: error: implicit declaration of function
>     >> ?HOST_PAGE_ALIGN? [-Werror=implicit-function-declaration]
>     >>   297 | HOST_PAGE_ALIGN(CRB_CTRL_CMD_SIZE));
>     >>       |                                 ^~~~~~~~~~~~~~~
>     >> ../hw/tpm/tpm_crb.c:297:33: error: nested extern declaration of
>     >> ?HOST_PAGE_ALIGN? [-Werror=nested-externs]
>     >> cc1: all warnings being treated as errors
>     >
>     > Do you have
>     > b269a70810a  exec/cpu: Make host pages variables / macros 'target
>     > agnostic' in your tree?
>     I may have missed your reply. Did you have that dependency? Were you
>     able to compile eventually?
> 
>     Besides, do you have any opinion overall about the relevance of
>     transforming the CRB ctrl cmd region into a RAM device wrt the TPM spec?
> 
>     Again spec says:
> 
>     "
>     Including the control structure, the three memory areas comprise the
>     entirety of the CRB. There are no constraints on how those three memory
>     areas are provided. They can all be in system RAM, or all be in device
>     memory, or any combination.
>     "
>     
> (https://trustedcomputinggroup.org/wp-content/uploads/Mobile-Command-Response-Buffer-Interface-v2-r12-Specification_FINAL2.pdf
>     
> <https://trustedcomputinggroup.org/wp-content/uploads/Mobile-Command-Response-Buffer-Interface-v2-r12-Specification_FINAL2.pdf>)
> 
>     What was the rationale behind using RAM device for the PPI region?
> 
> 
> Is this the rationale you are looking for?
> https://gitlab.com/qemu-project/qemu/-/commit/3b97c01e9ccdfbd517a0fd631838d6252dbfa692
> <https://gitlab.com/qemu-project/qemu/-/commit/3b97c01e9ccdfbd517a0fd631838d6252dbfa692>
> 
>     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.
And did this mandate to use "ram_device" memory type instead of standard
system RAM.

As I understand the spec (statement above), the CRB areas can be
implemented as system RAM or device memory. So I want to understand why
using RAM device for the CRB is not a reasonable choice. By the way I
understand my motivation behind that change is a bit far-fetched and
aiming at fixing another issue, but well ;-)

Thanks

Eric
>  
> 
> 
>     There are some spurious warnings when using CRB with VFIO and that would
>     be nice to remove them one way or the other.
> 
>     Thanks
> 
>     Eric
>     >
>     > Thanks
>     >
>     > Eric
>     >>
>     >>
>     >>
>     >
> 
> 
> 
> 
> -- 
> Marc-André Lureau