Re: [PATCH] tpm_crb: mark command buffer as dirty on request completion

[Anthony PERARD]

On Mon, Apr 11, 2022 at 12:31:01PM -0400, Stefan Berger wrote:
> On 4/11/22 10:47, Anthony PERARD wrote:
> > From: Anthony PERARD <anthony.perard@citrix.com>
> The state of the registers is saved using this here:
> 
> static const VMStateDescription vmstate_tpm_crb = {
>     .name = "tpm-crb",
>     .pre_save = tpm_crb_pre_save,
>     .fields = (VMStateField[]) {
>         VMSTATE_UINT32_ARRAY(regs, CRBState, TPM_CRB_R_MAX),
>         VMSTATE_END_OF_LIST(),
>     }
> };
> 
> The buffer with the commands is not part of this. So likely it needs to be
> marked dirty but then I am not sure whether that is going to work if the
> response to a command on the CRB is only received when tpm_crb_pre_save() is
> called.. Maybe this buffer would have to be save explicitly in a .save
> function or also as part of vmstate_tpm_crb... ?

I did some research on migration of a guest with Xen toolstack, and I
think there is one last round of sending memory marked as dirty after we
call "xen-save-devices-state" (with the guest suspended), that's when
tpm_crb_pre_save() is called. Hopefully, when QEMU is in charge of
migration, it does the same thing and there would not be a need to save
the buffer in vmstate of this device.

Cheers,

-- 
Anthony PERARD