Messages in this thread | | | Date | Tue, 25 Oct 2022 10:30:56 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH Part2 v6 12/49] crypto: ccp: Add support to initialize the AMD-SP for SEV-SNP |
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On Fri, Oct 14, 2022 at 04:09:11PM -0500, Kalra, Ashish wrote: > Yes, we need to do: > > wbinvd_on_all_cpus(); > SNP_DF_FLUSH > > Need to ensure all the caches are clear before launching the first guest and > this has to be a combination of WBINVD and SNP_DF_FLUSH command.
Ok.
> > Why isn't this retval checked? > > From the SNP FW ABI specs, for the SNP_SHUTDOWN command: > > Firmware checks for every encryption capable ASID that the ASID is not in > use by a guest and a DF_FLUSH is not required. If a DF_FLUSH is required, > the firmware returns DFFLUSH_REQUIRED. > > Considering that SNP_SHUTDOWN command will check if DF_FLUSH was > required and if so, and not invoked before that command, returns > an error indicating that DFFLUSH is required. > > This way, we can cleverly avoid taking the error code path for > DF_FLUSH command here and instead let the SNP_SHUTDOWN command > failure below indicate if DF_FLUSH command failed. > > This also ensures that we always invoke SNP_SHUTDOWN command, > irrespective of SNP_DF_FLUSH command failure as SNP_DF_FLUSH may > actually not be required by the SHUTDOWN command.
This all sounds just silly. The proper way to do this is:
retry: ret = __sev_do_cmd_locked(SEV_CMD_SNP_SHUTDOWN, NULL, error); if (ret == DFFLUSH_REQUIRED) { ret = __sev_do_cmd_locked(SEV_CMD_SNP_DF_FLUSH, NULL, NULL); if (ret) "... DF_FLUSH failed...";
goto retry; }
I'm assuming here the firmware is smart enough to not keep returning DFFLUSH_REQUIRED constantly and cause an endless loop.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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