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hptw: Eliminated A and D bit faults while walking page table, per spec

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This commit is contained in:
David Harris 2021-07-17 14:29:20 -04:00
parent 90c5312f85
commit 714eef4a1a
1 changed files with 10 additions and 10 deletions
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18
wally-pipelined/src/mmu/pagetablewalker.sv
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@ -76,8 +76,8 @@ module pagetablewalker
logic [`PA_BITS-1:0] TranslationPAdr;
logic [`PPN_BITS-1:0] CurrentPPN;
logic MemWrite;
logic Dirty, Accessed, Global, User, Executable, Writable, Readable, Valid;
logic ValidPTE, ADPageFault, MegapageMisaligned, TerapageMisaligned, GigapageMisaligned, BadMegapage, LeafPTE;
logic Executable, Writable, Readable, Valid;
logic ValidPTE, MegapageMisaligned, TerapageMisaligned, GigapageMisaligned, BadMegapage, LeafPTE;
logic StartWalk;
logic EndWalk;
logic PRegEn;
@ -110,10 +110,10 @@ module pagetablewalker
assign EndWalk = (WalkerState == LEAF) || (WalkerState == FAULT);
// Assign PTE descriptors common across all XLEN values
assign {Dirty, Accessed, Global, User, Executable, Writable, Readable, Valid} = CurrentPTE[7:0];
assign LeafPTE = Executable | Readable; // leaf PTE never has only Writable
// For non-leaf PTEs, D, A, U bits are reserved and ignored. They do not cause faults while walking the page table
assign {Executable, Writable, Readable, Valid} = CurrentPTE[3:0];
assign LeafPTE = Executable | Writable | Readable;
assign ValidPTE = Valid && ~(Writable && ~Readable);
assign ADPageFault = ~Accessed | (MemWrite & ~Dirty);
// Assign specific outputs to general outputs
// *** try to eliminate this duplication, but attempts caused MMU to hang
@ -211,25 +211,25 @@ module pagetablewalker
LEVEL3_SET_ADR: NextWalkerState = LEVEL3_WDV;
LEVEL3_WDV: if (HPTWStall) NextWalkerState = LEVEL3_WDV;
else NextWalkerState = LEVEL3;
LEVEL3: if (ValidPTE && LeafPTE && ~(TerapageMisaligned || ADPageFault)) NextWalkerState = LEAF;
LEVEL3: if (ValidPTE && LeafPTE && ~TerapageMisaligned) NextWalkerState = LEAF;
else if (ValidPTE && ~LeafPTE) NextWalkerState = LEVEL2_SET_ADR;
else NextWalkerState = FAULT;
LEVEL2_SET_ADR: NextWalkerState = LEVEL2_WDV;
LEVEL2_WDV: if (HPTWStall) NextWalkerState = LEVEL2_WDV;
else NextWalkerState = LEVEL2;
LEVEL2: if (ValidPTE && LeafPTE && ~(GigapageMisaligned || ADPageFault)) NextWalkerState = LEAF;
LEVEL2: if (ValidPTE && LeafPTE && ~GigapageMisaligned) NextWalkerState = LEAF;
else if (ValidPTE && ~LeafPTE) NextWalkerState = LEVEL1_SET_ADR;
else NextWalkerState = FAULT;
LEVEL1_SET_ADR: NextWalkerState = LEVEL1_WDV;
LEVEL1_WDV: if (HPTWStall) NextWalkerState = LEVEL1_WDV;
else NextWalkerState = LEVEL1;
LEVEL1: if (ValidPTE && LeafPTE && ~(MegapageMisaligned || ADPageFault)) NextWalkerState = LEAF;
LEVEL1: if (ValidPTE && LeafPTE && ~MegapageMisaligned) NextWalkerState = LEAF;
else if (ValidPTE && ~LeafPTE) NextWalkerState = LEVEL0_SET_ADR;
else NextWalkerState = FAULT;
LEVEL0_SET_ADR: NextWalkerState = LEVEL0_WDV;
LEVEL0_WDV: if (HPTWStall) NextWalkerState = LEVEL0_WDV;
else NextWalkerState = LEVEL0;
LEVEL0: if (ValidPTE && LeafPTE && ~ADPageFault) NextWalkerState = LEAF;
LEVEL0: if (ValidPTE && LeafPTE) NextWalkerState = LEAF;
else NextWalkerState = FAULT;
LEAF: NextWalkerState = IDLE;
FAULT: NextWalkerState = IDLE;