On Wed, 2023-06-07 at 09:05 -0700, Dave Hansen wrote:
> On 6/4/23 07:27, Kai Huang wrote:
> > + /*
> > + * Loop over TDX memory regions and fill out TDMRs to cover them.
> > + * To keep it simple, always try to use one TDMR to cover one
> > + * memory region.
> > + *
> > + * In practice TDX1.0 supports 64 TDMRs, which is big enough to
> > + * cover all memory regions in reality if the admin doesn't use
> > + * 'memmap' to create a bunch of discrete memory regions. When
> > + * there's a real problem, enhancement can be done to merge TDMRs
> > + * to reduce the final number of TDMRs.
> > + */
>
> Rather than focus in on one specific command-line parameter, let's just say:
>
> In practice TDX supports at least 64 TDMRs. A 2-socket system
> typically only consumes <NUMBER> of those. This code is dumb
> and simple and may use more TMDRs than is strictly required.
Thanks will do. Will take a look at machine to get the <NUMBER>.
>
> Let's also put a pr_warn() in here if we exceed, say 1/2 or maybe 3/4 of
> the 64. We'll hopefully start to get reports somewhat in advance if
> systems get close to the limit.
May I ask why this is useful? TDX module can only be initialized once, so if
not considering module runtime update case, the kernel can only get two results
for once:
1) Succeed to initialize: consumed TDMRs doesn't exceed maximum TDMRs
2) Fail to initialize: consumed TDMRs exceeds maximum TDMRs
What's the value of pr_warn() user when consumed TDMRs exceeds some threshold?
Anyway, if you want it, how does below code look?
static int fill_out_tdmrs(struct list_head *tmb_list,
struct tdmr_info_list *tdmr_list)
{
+ int consumed_tdmrs_threshold, tdmr_idx = 0;
struct tdx_memblock *tmb;
- int tdmr_idx = 0;
/*
* Loop over TDX memory regions and fill out TDMRs to cover them.
* To keep it simple, always try to use one TDMR to cover one
* memory region.
*
- * In practice TDX1.0 supports 64 TDMRs, which is big enough to
- * cover all memory regions in reality if the admin doesn't use
- * 'memmap' to create a bunch of discrete memory regions. When
- * there's a real problem, enhancement can be done to merge TDMRs
- * to reduce the final number of TDMRs.
+ * In practice TDX supports at least 64 TDMRs. A 2-socket system
+ * typically only consumes <NUMBER> of those. This code is dumb
+ * and simple and may use more TMDRs than is strictly required.
+ *
+ * Also set a threshold of consumed TDMRs, and pr_warn() to warn
+ * the user the system is getting close to the limit of supported
+ * number of TDMRs if the number of consumed TDMRs exceeds the
+ * threshold.
*/
+ consumed_tdmrs_threshold = tdmr_list->max_tdmrs * 3 / 4;
list_for_each_entry(tmb, tmb_list, list) {
struct tdmr_info *tdmr = tdmr_entry(tdmr_list, tdmr_idx);
u64 start, end;
@@ -463,6 +467,10 @@ static int fill_out_tdmrs(struct list_head *tmb_list,
return -ENOSPC;
}
+ if (tdmr_idx == consumed_tdmrs_threshold)
+ pr_warn("consumed TDMRs reaching limit: %d used
(out of %d)\n",
+ tdmr_idx, tdmr_list->max_tdmrs);
+
tdmr = tdmr_entry(tdmr_list, tdmr_idx);
}
