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MMU: Refetch PTE on access fault

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This is required by the architecture.  It means that the error bits
reported in DSISR or SRR1 now come from the permission/RC check done
on the refetched PTE rather than the TLB entry.  Unfortunately that
somewhat breaks the software-loaded TLB mode of operation in that
DSISR/SRR1 always report no PTE rather than permission error or
RC failure.

This also restructures the loadstore1 state machine a bit, combining
the FIRST_ACK_WAIT and LAST_ACK_WAIT states into a single state and
the MMU_LOOKUP_1ST and MMU_LOOKUP_LAST states likewise.  We now have a
'dwords_done' bit to say whether the first transfer of two (for an
unaligned access) has been done.

The cache paradox error (where a non-cacheable access finds a hit in
the cache) is now the only cause of DSI from the dcache.  This should
probably be a machine check rather than DSI in fact.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
pull/169/head
Paul Mackerras 4 years ago
parent f6a0d7f9da
commit 3eb07dc637
4 changed files with 103 additions and 85 deletions
Show Stats Download Patch File Download Diff File

18
common.vhdl
Unescape Escape View File

@ -263,26 +263,28 @@ package common is
data : std_ulogic_vector(63 downto 0); data : std_ulogic_vector(63 downto 0);
store_done : std_ulogic; store_done : std_ulogic;
error : std_ulogic; error : std_ulogic;
tlb_miss : std_ulogic; cache_paradox : std_ulogic;
perm_error : std_ulogic;
rc_error : std_ulogic;
end record; end record;


type Loadstore1ToMmuType is record type Loadstore1ToMmuType is record
valid : std_ulogic; valid : std_ulogic;
tlbie : std_ulogic; tlbie : std_ulogic;
mtspr : std_ulogic; mtspr : std_ulogic;
load : std_ulogic;
priv : std_ulogic;
sprn : std_ulogic_vector(3 downto 0); sprn : std_ulogic_vector(3 downto 0);
addr : std_ulogic_vector(63 downto 0); addr : std_ulogic_vector(63 downto 0);
rs : std_ulogic_vector(63 downto 0); rs : std_ulogic_vector(63 downto 0);
end record; end record;


type MmuToLoadstore1Type is record type MmuToLoadstore1Type is record
done : std_ulogic; done : std_ulogic;
invalid : std_ulogic; invalid : std_ulogic;
badtree : std_ulogic; badtree : std_ulogic;
segerr : std_ulogic; segerr : std_ulogic;
sprval : std_ulogic_vector(63 downto 0); perm_error : std_ulogic;
rc_error : std_ulogic;
sprval : std_ulogic_vector(63 downto 0);
end record; end record;


type MmuToDcacheType is record type MmuToDcacheType is record

29
dcache.vhdl
Unescape Escape View File

@ -179,6 +179,7 @@ architecture rtl of dcache is
OP_LOAD_MISS, -- Load missing cache OP_LOAD_MISS, -- Load missing cache
OP_LOAD_NC, -- Non-cachable load OP_LOAD_NC, -- Non-cachable load
OP_BAD, -- BAD: Cache hit on NC load/store OP_BAD, -- BAD: Cache hit on NC load/store
OP_TLB_ERR, -- TLB miss or protection/RC failure
OP_STORE_HIT, -- Store hitting cache OP_STORE_HIT, -- Store hitting cache
OP_STORE_MISS); -- Store missing cache OP_STORE_MISS); -- Store missing cache
@ -244,9 +245,7 @@ architecture rtl of dcache is


-- Signals to complete with error -- Signals to complete with error
error_done : std_ulogic; error_done : std_ulogic;
tlb_miss : std_ulogic; -- No entry found in TLB cache_paradox : std_ulogic;
perm_error : std_ulogic; -- Permissions don't allow access
rc_error : std_ulogic; -- Reference or change bit clear


-- completion signal for tlbie -- completion signal for tlbie
tlbie_done : std_ulogic; tlbie_done : std_ulogic;
@ -758,7 +757,7 @@ begin
when others => op := OP_NONE; when others => op := OP_NONE;
end case; end case;
else else
op := OP_BAD; op := OP_TLB_ERR;
end if; end if;
end if; end if;
req_op <= op; req_op <= op;
@ -829,9 +828,7 @@ begin
d_out.data <= cache_out(r1.hit_way); d_out.data <= cache_out(r1.hit_way);
d_out.store_done <= '0'; d_out.store_done <= '0';
d_out.error <= '0'; d_out.error <= '0';
d_out.tlb_miss <= '0'; d_out.cache_paradox <= '0';
d_out.perm_error <= '0';
d_out.rc_error <= '0';


-- Outputs to MMU -- Outputs to MMU
m_out.done <= r1.tlbie_done; m_out.done <= r1.tlbie_done;
@ -868,9 +865,7 @@ begin
if r1.error_done = '1' then if r1.error_done = '1' then
report "completing ld/st with error"; report "completing ld/st with error";
d_out.error <= '1'; d_out.error <= '1';
d_out.tlb_miss <= r1.tlb_miss; d_out.cache_paradox <= r1.cache_paradox;
d_out.perm_error <= r1.perm_error;
d_out.rc_error <= r1.rc_error;
d_out.valid <= '1'; d_out.valid <= '1';
end if; end if;


@ -1034,15 +1029,18 @@ begin
r1.hit_load_valid <= '0'; r1.hit_load_valid <= '0';
end if; end if;


if req_op = OP_BAD then if req_op = OP_TLB_ERR then
report "Signalling ld/st error valid_ra=" & std_ulogic'image(valid_ra) & report "Signalling ld/st error valid_ra=" & std_ulogic'image(valid_ra) &
" rc_ok=" & std_ulogic'image(rc_ok) & " perm_ok=" & std_ulogic'image(perm_ok); " rc_ok=" & std_ulogic'image(rc_ok) & " perm_ok=" & std_ulogic'image(perm_ok);
r1.error_done <= '1'; r1.error_done <= '1';
r1.tlb_miss <= not valid_ra; r1.cache_paradox <= '0';
r1.perm_error <= valid_ra and not perm_ok; elsif req_op = OP_BAD then
r1.rc_error <= valid_ra and perm_ok and not rc_ok; report "Signalling cache paradox";
r1.error_done <= '1';
r1.cache_paradox <= '1';
else else
r1.error_done <= '0'; r1.error_done <= '0';
r1.cache_paradox <= '0';
end if; end if;


-- complete tlbies and TLB loads in the third cycle -- complete tlbies and TLB loads in the third cycle
@ -1187,7 +1185,8 @@ begin
-- OP_NONE and OP_BAD do nothing -- OP_NONE and OP_BAD do nothing
-- OP_BAD was handled above already -- OP_BAD was handled above already
when OP_NONE => when OP_NONE =>
when OP_BAD => when OP_BAD =>
when OP_TLB_ERR =>
end case; end case;


when RELOAD_WAIT_ACK => when RELOAD_WAIT_ACK =>

114
loadstore1.vhdl
Unescape Escape View File

@ -38,11 +38,10 @@ architecture behave of loadstore1 is
-- State machine for unaligned loads/stores -- State machine for unaligned loads/stores
type state_t is (IDLE, -- ready for instruction type state_t is (IDLE, -- ready for instruction
SECOND_REQ, -- send 2nd request of unaligned xfer SECOND_REQ, -- send 2nd request of unaligned xfer
FIRST_ACK_WAIT, -- waiting for 1st ack from dcache ACK_WAIT, -- waiting for ack from dcache
LAST_ACK_WAIT, -- waiting for last ack from dcache
LD_UPDATE, -- writing rA with computed addr on load LD_UPDATE, -- writing rA with computed addr on load
MMU_LOOKUP_1ST, -- waiting for MMU to look up translation MMU_LOOKUP, -- waiting for MMU to look up translation
MMU_LOOKUP_LAST TLBIE_WAIT -- waiting for MMU to finish doing a tlbie
); );


type reg_stage_t is record type reg_stage_t is record
@ -66,6 +65,7 @@ architecture behave of loadstore1 is
virt_mode : std_ulogic; virt_mode : std_ulogic;
priv_mode : std_ulogic; priv_mode : std_ulogic;
state : state_t; state : state_t;
dwords_done : std_ulogic;
first_bytes : std_ulogic_vector(7 downto 0); first_bytes : std_ulogic_vector(7 downto 0);
second_bytes : std_ulogic_vector(7 downto 0); second_bytes : std_ulogic_vector(7 downto 0);
dar : std_ulogic_vector(63 downto 0); dar : std_ulogic_vector(63 downto 0);
@ -230,6 +230,7 @@ begin
v.load := '0'; v.load := '0';
v.dcbz := '0'; v.dcbz := '0';
v.tlbie := '0'; v.tlbie := '0';
v.dwords_done := '0';
case l_in.op is case l_in.op is
when OP_STORE => when OP_STORE =>
req := '1'; req := '1';
@ -241,7 +242,9 @@ begin
v.dcbz := '1'; v.dcbz := '1';
when OP_TLBIE => when OP_TLBIE =>
mmureq := '1'; mmureq := '1';
stall := '1';
v.tlbie := '1'; v.tlbie := '1';
v.state := TLBIE_WAIT;
when OP_MFSPR => when OP_MFSPR =>
done := '1'; done := '1';
mfspr := '1'; mfspr := '1';
@ -318,15 +321,11 @@ begin
if req = '1' then if req = '1' then
stall := '1'; stall := '1';
if long_sel(15 downto 8) = "00000000" then if long_sel(15 downto 8) = "00000000" then
v.state := LAST_ACK_WAIT; v.state := ACK_WAIT;
else else
v.state := SECOND_REQ; v.state := SECOND_REQ;
end if; end if;
end if; end if;
if mmureq = '1' then
stall := '1';
v.state := LAST_ACK_WAIT;
end if;
end if; end if;


when SECOND_REQ => when SECOND_REQ =>
@ -334,37 +333,58 @@ begin
byte_sel := r.second_bytes; byte_sel := r.second_bytes;
req := '1'; req := '1';
stall := '1'; stall := '1';
v.state := FIRST_ACK_WAIT; v.state := ACK_WAIT;


when FIRST_ACK_WAIT => when ACK_WAIT =>
stall := '1'; stall := '1';
if d_in.valid = '1' then if d_in.valid = '1' then
if d_in.error = '1' then if d_in.error = '1' then
-- dcache will discard the second request -- dcache will discard the second request if it
addr := r.addr; -- gets an error on the 1st of two requests
if d_in.tlb_miss = '1' then if r.dwords_done = '1' then
-- give it to the MMU to look up addr := next_addr;
mmureq := '1';
v.state := MMU_LOOKUP_1ST;
else else
addr := r.addr;
end if;
if d_in.cache_paradox = '1' then
-- signal an interrupt straight away -- signal an interrupt straight away
exception := '1'; exception := '1';
dsisr(63 - 36) := d_in.perm_error;
dsisr(63 - 38) := not r.load; dsisr(63 - 38) := not r.load;
dsisr(63 - 45) := d_in.rc_error; -- XXX there is no architected bit for this
dsisr(63 - 35) := d_in.cache_paradox;
v.state := IDLE; v.state := IDLE;
else
-- Look up the translation for TLB miss
-- and also for permission error and RC error
-- in case the PTE has been updated.
mmureq := '1';
v.state := MMU_LOOKUP;
end if; end if;
else else
v.state := LAST_ACK_WAIT; if two_dwords = '1' and r.dwords_done = '0' then
if r.load = '1' then v.dwords_done := '1';
v.load_data := data_permuted; if r.load = '1' then
v.load_data := data_permuted;
end if;
else
write_enable := r.load;
if r.load = '1' and r.update = '1' then
-- loads with rA update need an extra cycle
v.state := LD_UPDATE;
else
-- stores write back rA update in this cycle
do_update := r.update;
stall := '0';
done := '1';
v.state := IDLE;
end if;
end if; end if;
end if; end if;
end if; end if;


when MMU_LOOKUP_1ST | MMU_LOOKUP_LAST => when MMU_LOOKUP =>
stall := '1'; stall := '1';
if two_dwords = '1' and r.state = MMU_LOOKUP_LAST then if r.dwords_done = '1' then
addr := next_addr; addr := next_addr;
byte_sel := r.second_bytes; byte_sel := r.second_bytes;
else else
@ -372,58 +392,28 @@ begin
byte_sel := r.first_bytes; byte_sel := r.first_bytes;
end if; end if;
if m_in.done = '1' then if m_in.done = '1' then
if m_in.invalid = '0' and m_in.badtree = '0' and m_in.segerr = '0' then if m_in.invalid = '0' and m_in.perm_error = '0' and m_in.rc_error = '0' and
m_in.badtree = '0' and m_in.segerr = '0' then
-- retry the request now that the MMU has installed a TLB entry -- retry the request now that the MMU has installed a TLB entry
req := '1'; req := '1';
if r.state = MMU_LOOKUP_1ST then if two_dwords = '1' and r.dwords_done = '0' then
v.state := SECOND_REQ; v.state := SECOND_REQ;
else else
v.state := LAST_ACK_WAIT; v.state := ACK_WAIT;
end if; end if;
else else
exception := '1'; exception := '1';
dsisr(63 - 33) := m_in.invalid; dsisr(63 - 33) := m_in.invalid;
dsisr(63 - 36) := m_in.perm_error;
dsisr(63 - 38) := not r.load; dsisr(63 - 38) := not r.load;
dsisr(63 - 44) := m_in.badtree; dsisr(63 - 44) := m_in.badtree;
dsisr(63 - 45) := m_in.rc_error;
v.state := IDLE; v.state := IDLE;
end if; end if;
end if; end if;


when LAST_ACK_WAIT => when TLBIE_WAIT =>
stall := '1'; stall := '1';
if d_in.valid = '1' then
if d_in.error = '1' then
if two_dwords = '1' then
addr := next_addr;
else
addr := r.addr;
end if;
if d_in.tlb_miss = '1' then
-- give it to the MMU to look up
mmureq := '1';
v.state := MMU_LOOKUP_LAST;
else
-- signal an interrupt straight away
exception := '1';
dsisr(63 - 36) := d_in.perm_error;
dsisr(63 - 38) := not r.load;
dsisr(63 - 45) := d_in.rc_error;
v.state := IDLE;
end if;
else
write_enable := r.load;
if r.load = '1' and r.update = '1' then
-- loads with rA update need an extra cycle
v.state := LD_UPDATE;
else
-- stores write back rA update in this cycle
do_update := r.update;
stall := '0';
done := '1';
v.state := IDLE;
end if;
end if;
end if;
if m_in.done = '1' then if m_in.done = '1' then
-- tlbie is finished -- tlbie is finished
stall := '0'; stall := '0';
@ -451,6 +441,8 @@ begin


-- Update outputs to MMU -- Update outputs to MMU
m_out.valid <= mmureq; m_out.valid <= mmureq;
m_out.load <= r.load;
m_out.priv <= r.priv_mode;
m_out.tlbie <= v.tlbie; m_out.tlbie <= v.tlbie;
m_out.mtspr <= mmu_mtspr; m_out.mtspr <= mmu_mtspr;
m_out.sprn <= sprn(3 downto 0); m_out.sprn <= sprn(3 downto 0);

27
mmu.vhdl
Unescape Escape View File

@ -36,6 +36,8 @@ architecture behave of mmu is
type reg_stage_t is record type reg_stage_t is record
-- latched request from loadstore1 -- latched request from loadstore1
valid : std_ulogic; valid : std_ulogic;
store : std_ulogic;
priv : std_ulogic;
addr : std_ulogic_vector(63 downto 0); addr : std_ulogic_vector(63 downto 0);
-- internal state -- internal state
state : state_t; state : state_t;
@ -47,6 +49,8 @@ architecture behave of mmu is
invalid : std_ulogic; invalid : std_ulogic;
badtree : std_ulogic; badtree : std_ulogic;
segerror : std_ulogic; segerror : std_ulogic;
perm_err : std_ulogic;
rc_error : std_ulogic;
end record; end record;


signal r, rin : reg_stage_t; signal r, rin : reg_stage_t;
@ -166,6 +170,8 @@ begin
variable pte : std_ulogic_vector(63 downto 0); variable pte : std_ulogic_vector(63 downto 0);
variable data : std_ulogic_vector(63 downto 0); variable data : std_ulogic_vector(63 downto 0);
variable nonzero : std_ulogic; variable nonzero : std_ulogic;
variable perm_ok : std_ulogic;
variable rc_ok : std_ulogic;
begin begin
v := r; v := r;
v.valid := '0'; v.valid := '0';
@ -174,6 +180,8 @@ begin
v.invalid := '0'; v.invalid := '0';
v.badtree := '0'; v.badtree := '0';
v.segerror := '0'; v.segerror := '0';
v.perm_err := '0';
v.rc_error := '0';
tlb_load := '0'; tlb_load := '0';
tlbie_req := '0'; tlbie_req := '0';


@ -196,6 +204,8 @@ begin


if l_in.valid = '1' then if l_in.valid = '1' then
v.addr := l_in.addr; v.addr := l_in.addr;
v.store := not l_in.load;
v.priv := l_in.priv;
if l_in.tlbie = '1' then if l_in.tlbie = '1' then
dcreq := '1'; dcreq := '1';
tlbie_req := '1'; tlbie_req := '1';
@ -247,7 +257,20 @@ begin
if data(63) = '1' then if data(63) = '1' then
-- test leaf bit -- test leaf bit
if data(62) = '1' then if data(62) = '1' then
v.state := RADIX_LOAD_TLB; -- check permissions and RC bits
perm_ok := '0';
if r.priv = '1' or data(3) = '0' then
perm_ok := data(1) or (data(2) and not r.store);
end if;
rc_ok := data(8) and (data(7) or not r.store);
if perm_ok = '1' and rc_ok = '1' then
v.state := RADIX_LOAD_TLB;
else
v.state := RADIX_ERROR;
v.perm_err := not perm_ok;
-- permission error takes precedence over RC error
v.rc_error := perm_ok;
end if;
else else
mbits := unsigned('0' & data(4 downto 0)); mbits := unsigned('0' & data(4 downto 0));
if mbits < 5 or mbits > 16 or mbits > r.shift then if mbits < 5 or mbits > 16 or mbits > r.shift then
@ -297,6 +320,8 @@ begin
l_out.invalid <= r.invalid; l_out.invalid <= r.invalid;
l_out.badtree <= r.badtree; l_out.badtree <= r.badtree;
l_out.segerr <= r.segerror; l_out.segerr <= r.segerror;
l_out.perm_error <= r.perm_err;
l_out.rc_error <= r.rc_error;


d_out.valid <= dcreq; d_out.valid <= dcreq;
d_out.tlbie <= tlbie_req; d_out.tlbie <= tlbie_req;

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