PTW: check all reserved bits for non-leaf ptes #3408
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@aswaterman Would you mind take a quick look at this as well? Rocket-chip is missing the conditions for non-leaf page-fault. It checks the conditions in table but fails to report it as a page-fault. Thanks. |
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cc @ingallsj again, but this looks right to me.
I'd suggest the name isReservedIfNonLeaf.
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Looking, and attempting to reproduce the bug and fix ourselves, too. Standby. |
Non-leaf PTEs should not have any of D, A, and U bits set, otherwise a page-fault exception is raised.
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Changed the name to |
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Because the definition of a non-leaf "table" PTE is that the R,W,X permission bits are zeroes "off", the L1TLB (ITLB/DTLB) then goes on to report a page fault, even though the PTW response did not explicitly include the pf bit set.
So we think that this change would add redundant logic to what the L1TLB (ITLB/DTLB) already performs, and we don't think there is a bug that this change fixes.
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After double-checking the case, I found you are right and this bug depends on a wrong patch for #3407. Before I submit the final and correct PR for that, I had a bad patch trying to fix #3407. This bug is only feasible in that version. Sorry for the confusion and thanks for your work. I'll close this PR. |
Non-leaf PTEs should not have any of D, A, and U bits set, otherwise a page-fault exception is raised.
Previously rocket-chip is missing the condition for D, A, and U bits.
Related issue:
Type of change: bug report
Impact: API modification
Development Phase: implementation
Release Notes
See #3402 (comment) for more information on the bug.