fix(PTW): Fix exception handle logic when both pf and af occur#4422
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good-circle merged 1 commit intomasterfrom Mar 23, 2025
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fix(PTW): Fix exception handle logic when both pf and af occur#4422good-circle merged 1 commit intomasterfrom
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Please do not merge now |
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…ult occur In the previous design, every time a page table entry was fetched from memory, a PMP check was performed on the physical address of the next-level page table. However, for cases requiring Stage-2 address translation or when a page fault occurs during the page table fetch, a PMP check is unnecessary. Performing a PMP check in these cases could lead to false access fault reports. This commit fixes the issue. Future work: The current exception handling logic is messy and unsustainable. A complete refactor of this code is needed in the future, rather than continuing to add patches.
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Already tested kvm on simulator and can be merged now |
cebarobot
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Future work: The current exception handling logic is messy and unsustainable. A complete refactor of this code is needed in the future, rather than continuing to add patches.
I totally agree with this.
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In #4422, For the virtualized allStage scenario, we attempt to suppress PMP checks until the G-stage translation result is returned. However, the approach used in #4422 is to try ignoring the `accessFault` result when `io.hptw.req.valid` is asserted. In reality, the `accessFault` signal remains valid because it is implemented as a `RegEnable`. Therefore, we need to prevent `sent_to_pmp` from being asserted when sending the G-stage translation request to HPTW. To address this, we introduce the `vs_finish` signal. When `vs_finish` is `true.B`, `sent_to_pmp` will be false, thus avoiding false `accessFault` reports.
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In #4422, For the virtualized allStage scenario, we attempt to suppress PMP checks until the G-stage translation result is returned. However, the approach used in #4422 is to try ignoring the `accessFault` result when `io.hptw.req.valid` is asserted. In reality, the `accessFault` signal remains valid because it is implemented as a `RegEnable`. Therefore, we need to prevent `sent_to_pmp` from being asserted when sending the G-stage translation request to HPTW. To address this, we introduce the `vs_finish` signal. When `vs_finish` is `true.B`, `sent_to_pmp` will be false, thus avoiding false `accessFault` reports.
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In the previous design, every time a page table entry was fetched from memory, a PMP check was performed on the physical address of the next-level page table. However, for cases requiring Stage-2 address translation or when a page fault occurs during the page table fetch, a PMP check is unnecessary. Performing a PMP check in these cases could lead to false access fault reports. This commit fixes the issue.
Future work: The current exception handling logic is messy and unsustainable. A complete refactor of this code is needed in the future, rather than continuing to add patches.