On 5/12/25 3:00 AM, Sairaj Kodilkar wrote:
On 5/2/2025 7:46 AM, Alejandro Jimenez wrote:
- if (pte & AMDVI_DEV_TRANSLATION_VALID) {
- level = get_pte_translation_mode(pte);
- if (level >= 7) {
- trace_amdvi_mode_invalid(level, addr);
+ if (!(pte & AMDVI_DEV_TRANSLATION_VALID)) {
+ /*
+ * A DTE with V=1, TV=0 does not have a valid Page Table Root
Pointer.
+ * An IOMMU processing a request that requires a table walk
terminates
+ * the walk when it encounters this condition. Do the same
and return
+ * instead of assuming that the address is forwarded without
translation
+ * i.e. the passthrough case, as it is done for the case
where DTE[V]=0.
+ */
+ return;
+ }
Above change seems redundant since caller of the amdvi_page_walk(),
amdvi_do_translate() checks the return value of amdvi_as_to_dte().
amdvi_do_translate() returns when it encounters -AMDVI_FR_DTE_TV and
does not call amdvi_page_walk().
It is perhaps redundant at this point for the reason you mention, as we
are already checking the DTE for all sorts of conditions earlier.
But I would like to leave it in since it serves as a good validation
that any future callers of amdvi_page_walk(), which might not check or
care about the return of amdvi_as_to_dte(), are passing a DTE that
specifically supports a page walk, which is exactly what this function
needs to proceed. Plus it provides a nice place to place the comment
detailing the IOMMU behavior in such cases.
If you are concerned about efficiency, this is already not a very fast
path, and the 5 assembly instructions this check takes (with a non-debug
build I think is ~2 instructions) will certainly not be what brings the
performance down :).
Alejandro
Regards
Sairaj Kodilkar
