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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>
This commit is contained in:
Paul Mackerras 2020-05-06 20:21:01 +10:00
parent f6a0d7f9da
commit 3eb07dc637
4 changed files with 103 additions and 85 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
common.vhdl
View File

@ -263,26 +263,28 @@ package common is
data : std_ulogic_vector(63 downto 0);
store_done : std_ulogic;
error : std_ulogic;
tlb_miss : std_ulogic;
perm_error : std_ulogic;
rc_error : std_ulogic;
cache_paradox : std_ulogic;
end record;
type Loadstore1ToMmuType is record
valid : std_ulogic;
tlbie : std_ulogic;
mtspr : std_ulogic;
load : std_ulogic;
priv : std_ulogic;
sprn : std_ulogic_vector(3 downto 0);
addr : std_ulogic_vector(63 downto 0);
rs : std_ulogic_vector(63 downto 0);
end record;
type MmuToLoadstore1Type is record
done : std_ulogic;
invalid : std_ulogic;
badtree : std_ulogic;
segerr : std_ulogic;
sprval : std_ulogic_vector(63 downto 0);
done : std_ulogic;
invalid : std_ulogic;
badtree : std_ulogic;
segerr : std_ulogic;
perm_error : std_ulogic;
rc_error : std_ulogic;
sprval : std_ulogic_vector(63 downto 0);
end record;
type MmuToDcacheType is record

29
dcache.vhdl
View File

@ -179,6 +179,7 @@ architecture rtl of dcache is
OP_LOAD_MISS, -- Load missing cache
OP_LOAD_NC, -- Non-cachable load
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_MISS); -- Store missing cache
@ -244,9 +245,7 @@ architecture rtl of dcache is
-- Signals to complete with error
error_done : std_ulogic;
tlb_miss : std_ulogic; -- No entry found in TLB
perm_error : std_ulogic; -- Permissions don't allow access
rc_error : std_ulogic; -- Reference or change bit clear
cache_paradox : std_ulogic;
-- completion signal for tlbie
tlbie_done : std_ulogic;
@ -758,7 +757,7 @@ begin
when others => op := OP_NONE;
end case;
else
op := OP_BAD;
op := OP_TLB_ERR;
end if;
end if;
req_op <= op;
@ -829,9 +828,7 @@ begin
d_out.data <= cache_out(r1.hit_way);
d_out.store_done <= '0';
d_out.error <= '0';
d_out.tlb_miss <= '0';
d_out.perm_error <= '0';
d_out.rc_error <= '0';
d_out.cache_paradox <= '0';
-- Outputs to MMU
m_out.done <= r1.tlbie_done;
@ -868,9 +865,7 @@ begin
if r1.error_done = '1' then
report "completing ld/st with error";
d_out.error <= '1';
d_out.tlb_miss <= r1.tlb_miss;
d_out.perm_error <= r1.perm_error;
d_out.rc_error <= r1.rc_error;
d_out.cache_paradox <= r1.cache_paradox;
d_out.valid <= '1';
end if;
@ -1034,15 +1029,18 @@ begin
r1.hit_load_valid <= '0';
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) &
" rc_ok=" & std_ulogic'image(rc_ok) & " perm_ok=" & std_ulogic'image(perm_ok);
r1.error_done <= '1';
r1.tlb_miss <= not valid_ra;
r1.perm_error <= valid_ra and not perm_ok;
r1.rc_error <= valid_ra and perm_ok and not rc_ok;
r1.cache_paradox <= '0';
elsif req_op = OP_BAD then
report "Signalling cache paradox";
r1.error_done <= '1';
r1.cache_paradox <= '1';
else
r1.error_done <= '0';
r1.cache_paradox <= '0';
end if;
-- complete tlbies and TLB loads in the third cycle
@ -1187,7 +1185,8 @@ begin
-- OP_NONE and OP_BAD do nothing
-- OP_BAD was handled above already
when OP_NONE =>
when OP_BAD =>
when OP_BAD =>
when OP_TLB_ERR =>
end case;
when RELOAD_WAIT_ACK =>

114
loadstore1.vhdl
View File

@ -38,11 +38,10 @@ architecture behave of loadstore1 is
-- State machine for unaligned loads/stores
type state_t is (IDLE, -- ready for instruction
SECOND_REQ, -- send 2nd request of unaligned xfer
FIRST_ACK_WAIT, -- waiting for 1st ack from dcache
LAST_ACK_WAIT, -- waiting for last ack from dcache
ACK_WAIT, -- waiting for ack from dcache
LD_UPDATE, -- writing rA with computed addr on load
MMU_LOOKUP_1ST, -- waiting for MMU to look up translation
MMU_LOOKUP_LAST
MMU_LOOKUP, -- waiting for MMU to look up translation
TLBIE_WAIT -- waiting for MMU to finish doing a tlbie
);
type reg_stage_t is record
@ -66,6 +65,7 @@ architecture behave of loadstore1 is
virt_mode : std_ulogic;
priv_mode : std_ulogic;
state : state_t;
dwords_done : std_ulogic;
first_bytes : std_ulogic_vector(7 downto 0);
second_bytes : std_ulogic_vector(7 downto 0);
dar : std_ulogic_vector(63 downto 0);
@ -230,6 +230,7 @@ begin
v.load := '0';
v.dcbz := '0';
v.tlbie := '0';
v.dwords_done := '0';
case l_in.op is
when OP_STORE =>
req := '1';
@ -241,7 +242,9 @@ begin
v.dcbz := '1';
when OP_TLBIE =>
mmureq := '1';
stall := '1';
v.tlbie := '1';
v.state := TLBIE_WAIT;
when OP_MFSPR =>
done := '1';
mfspr := '1';
@ -318,15 +321,11 @@ begin
if req = '1' then
stall := '1';
if long_sel(15 downto 8) = "00000000" then
v.state := LAST_ACK_WAIT;
v.state := ACK_WAIT;
else
v.state := SECOND_REQ;
end if;
end if;
if mmureq = '1' then
stall := '1';
v.state := LAST_ACK_WAIT;
end if;
end if;
when SECOND_REQ =>
@ -334,37 +333,58 @@ begin
byte_sel := r.second_bytes;
req := '1';
stall := '1';
v.state := FIRST_ACK_WAIT;
v.state := ACK_WAIT;
when FIRST_ACK_WAIT =>
when ACK_WAIT =>
stall := '1';
if d_in.valid = '1' then
if d_in.error = '1' then
-- dcache will discard the second request
addr := r.addr;
if d_in.tlb_miss = '1' then
-- give it to the MMU to look up
mmureq := '1';
v.state := MMU_LOOKUP_1ST;
-- dcache will discard the second request if it
-- gets an error on the 1st of two requests
if r.dwords_done = '1' then
addr := next_addr;
else
addr := r.addr;
end if;
if d_in.cache_paradox = '1' then
-- 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;
-- XXX there is no architected bit for this
dsisr(63 - 35) := d_in.cache_paradox;
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;
else
v.state := LAST_ACK_WAIT;
if r.load = '1' then
v.load_data := data_permuted;
if two_dwords = '1' and r.dwords_done = '0' then
v.dwords_done := '1';
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;
when MMU_LOOKUP_1ST | MMU_LOOKUP_LAST =>
when MMU_LOOKUP =>
stall := '1';
if two_dwords = '1' and r.state = MMU_LOOKUP_LAST then
if r.dwords_done = '1' then
addr := next_addr;
byte_sel := r.second_bytes;
else
@ -372,58 +392,28 @@ begin
byte_sel := r.first_bytes;
end if;
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
req := '1';
if r.state = MMU_LOOKUP_1ST then
if two_dwords = '1' and r.dwords_done = '0' then
v.state := SECOND_REQ;
else
v.state := LAST_ACK_WAIT;
v.state := ACK_WAIT;
end if;
else
exception := '1';
dsisr(63 - 33) := m_in.invalid;
dsisr(63 - 36) := m_in.perm_error;
dsisr(63 - 38) := not r.load;
dsisr(63 - 44) := m_in.badtree;
dsisr(63 - 45) := m_in.rc_error;
v.state := IDLE;
end if;
end if;
when LAST_ACK_WAIT =>
when TLBIE_WAIT =>
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
-- tlbie is finished
stall := '0';
@ -451,6 +441,8 @@ begin
-- Update outputs to MMU
m_out.valid <= mmureq;
m_out.load <= r.load;
m_out.priv <= r.priv_mode;
m_out.tlbie <= v.tlbie;
m_out.mtspr <= mmu_mtspr;
m_out.sprn <= sprn(3 downto 0);

27
mmu.vhdl
View File

@ -36,6 +36,8 @@ architecture behave of mmu is
type reg_stage_t is record
-- latched request from loadstore1
valid : std_ulogic;
store : std_ulogic;
priv : std_ulogic;
addr : std_ulogic_vector(63 downto 0);
-- internal state
state : state_t;
@ -47,6 +49,8 @@ architecture behave of mmu is
invalid : std_ulogic;
badtree : std_ulogic;
segerror : std_ulogic;
perm_err : std_ulogic;
rc_error : std_ulogic;
end record;
signal r, rin : reg_stage_t;
@ -166,6 +170,8 @@ begin
variable pte : std_ulogic_vector(63 downto 0);
variable data : std_ulogic_vector(63 downto 0);
variable nonzero : std_ulogic;
variable perm_ok : std_ulogic;
variable rc_ok : std_ulogic;
begin
v := r;
v.valid := '0';
@ -174,6 +180,8 @@ begin
v.invalid := '0';
v.badtree := '0';
v.segerror := '0';
v.perm_err := '0';
v.rc_error := '0';
tlb_load := '0';
tlbie_req := '0';
@ -196,6 +204,8 @@ begin
if l_in.valid = '1' then
v.addr := l_in.addr;
v.store := not l_in.load;
v.priv := l_in.priv;
if l_in.tlbie = '1' then
dcreq := '1';
tlbie_req := '1';
@ -247,7 +257,20 @@ begin
if data(63) = '1' then
-- test leaf bit
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
mbits := unsigned('0' & data(4 downto 0));
if mbits < 5 or mbits > 16 or mbits > r.shift then
@ -297,6 +320,8 @@ begin
l_out.invalid <= r.invalid;
l_out.badtree <= r.badtree;
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.tlbie <= tlbie_req;