Re: [PATCH v19 038/130] KVM: TDX: create/destroy VM structure

Isaku Yamahata
2024-03-25T21:48:50Z

On Mon, Mar 25, 2024 at 05:58:47PM +0800,
Binbin Wu <binbin.wu@linux.intel.com> wrote:

> > +static void tdx_clear_page(unsigned long page_pa)
> > +{
> > + const void *zero_page = (const void *) __va(page_to_phys(ZERO_PAGE(0)));
> > + void *page = __va(page_pa);
> > + unsigned long i;
> > +
> > + /*
> > + * When re-assign one page from old keyid to a new keyid, MOVDIR64B is
> > + * required to clear/write the page with new keyid to prevent integrity
> > + * error when read on the page with new keyid.
> > + *
> > + * clflush doesn't flush cache with HKID set. The cache line could be
> > + * poisoned (even without MKTME-i), clear the poison bit.
> > + */
> > + for (i = 0; i < PAGE_SIZE; i += 64)
> > + movdir64b(page + i, zero_page);
> > + /*
> > + * MOVDIR64B store uses WC buffer. Prevent following memory reads
> > + * from seeing potentially poisoned cache.
> > + */
> > + __mb();
>
> Is __wmb() sufficient for this case?

I don't think so because sfence is for other store. Here we care other load.

> > +
> > +static int tdx_do_tdh_mng_key_config(void *param)
> > +{
> > + hpa_t *tdr_p = param;
> > + u64 err;
> > +
> > + do {
> > + err = tdh_mng_key_config(*tdr_p);
> > +
> > + /*
> > + * If it failed to generate a random key, retry it because this
> > + * is typically caused by an entropy error of the CPU's random
>
> Here you say "typically", is there other cause and is it safe to loop on
> retry?

No as long as I know. the TDX module returns KEY_GENERATION_FAILED only when
rdrnd (or equivalent) failed. But I don't know the future.

Let's delete "tyepically" because it seems confusing.
--
Isaku Yamahata <isaku.yamahata@intel.com>