On Tue, Nov 07, 2023 at 01:00:00PM -0600, Kalra, Ashish wrote:
> > First of all, use the APM bit name here pls: MtrrFixDramModEn.
> >
> > And then, for the life of me, I can't find any mention in the APM why
> > this bit is needed. Neither in "15.36.2 Enabling SEV-SNP" nor in
> > "15.34.3 Enabling SEV".
> >
> > Looking at the bit defintions of WrMem an RdMem - read and write
> > requests get directed to system memory instead of MMIO so I guess you
> > don't want to be able to write MMIO for certain physical ranges when SNP
> > is enabled but it'll be good to have this properly explained instead of
> > a "this must happen" information-less sentence.
>
> This is a per-requisite for SNP_INIT as per the SNP Firmware ABI
> specifications, section 8.8.2:
Did you even read the text you're responding to?
> > This looks backwards. AFAICT, the IOMMU code should call arch code to
> > enable SNP at the right time, not the other way around - arch code
> > calling driver code.
> >
> > Especially if the SNP table enablement depends on some exact IOMMU
> > init_state:
> >
> > if (init_state > IOMMU_ENABLED) {
> > pr_err("SNP: Too late to enable SNP for IOMMU.\n");
> >
> >
>
> This is again as per SNP_INIT requirements, that SNP support is enabled in
> the IOMMU before SNP_INIT is done. The above function snp_rmptable_init()
> only calls the IOMMU driver to enable SNP support when it has detected and
> enabled platform support for SNP.
>v
> It is not that IOMMU driver has to call the arch code to enable SNP at the
> right time but it is the other way around that once platform support for SNP
> is enabled then the IOMMU driver has to be called to enable the same for the
> IOMMU and this needs to be done before the CCP driver is loaded and does
> SNP_INIT.
You again didn't read the text you're responding to.
Arch code does not call drivers - arch code sets up the arch and
provides facilities which the drivers use.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
