add extra information into exception reporting (#373)

We need to have the exception faulting address when a CHERI data memory
access faults.
Not having so is causing problems, so this adds two fields:

mtval.CAP_IDX - which cap caused the fault
mtval2 - XLEN wide address which faulted (already a standard CSR)
stval2 - as mtval2

---------

Signed-off-by: Tariq Kurd <[email protected]>
Co-authored-by: Andres Amaya Garcia <[email protected]>

src/hypervisor-integration.adoc

@@ -164,6 +164,36 @@ present when the implementation supports {cheri_default_ext_name}.
 .Virtual supervisor trap default capability register
 include::img/vstdcreg.edn[]
 
+[#vstval,reftext="vstval"]
+=== Virtual Supervisor Trap Value Register (vstval)
+
+The <<vstval>> register is an SXLEN-bit read-write register.
+
+When a fault is taken into VS-mode <<vstval>> is updated as for <<stval>> for all CHERI exceptions.
+
+.Virtual supervisor trap value register
+[#vstval-format]
+include::img/vstvalreg.edn[]
+
+
+[#vstval2,reftext="vstval2"]
+=== Virtual Supervisor Trap Value Register 2 (vstval2)
+
+The <<vstval2>> register is a VSXLEN-bit read-write register.
+
+The CSR address is 0x24b.
+
+When a fault is taken into VS-mode <<vstval2>> is updated as for <<mtval2>> for all CHERI exceptions.
+It is set to zero in all other cases.
+
+NOTE: This is not a standard RISC-V CSR, but <<mtval2>> is. 0x24b is the regular location for the CSR.
+
+<<vstval2>> holds the same set of values that <<stval2>> can hold.
+
+.Virtual supervisor trap value register 2
+[#vstval2-format]
+include::img/vstval2reg.edn[]
+
 === Existing Hypervisor Load and Store Instructions
 
 The hypervisor extension defines several integer load and store instructions

src/img/mtval2reg.edn

@@ -0,0 +1,14 @@
+[bytefield]
+----
+(defattrs :plain [:plain {:font-family "M+ 1p Fallback" :font-size 24}])
+(def row-height 40)
+(def row-header-fn nil)
+(def left-margin 100)
+(def right-margin 100)
+(def boxes-per-row 32)
+(draw-column-headers {:height 20 :font-size 18 :labels (reverse ["0" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "MXLEN-1"])})
+
+(draw-box "Addr"   {:span 32})
+
+(draw-box "MXLEN" {:span 32 :borders {}})
+----

src/img/stval2reg.edn

@@ -0,0 +1,14 @@
+[bytefield]
+----
+(defattrs :plain [:plain {:font-family "M+ 1p Fallback" :font-size 24}])
+(def row-height 40)
+(def row-header-fn nil)
+(def left-margin 100)
+(def right-margin 100)
+(def boxes-per-row 32)
+(draw-column-headers {:height 20 :font-size 18 :labels (reverse ["0" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "SXLEN-1"])})
+
+(draw-box "Addr"   {:span 32})
+
+(draw-box "SXLEN" {:span 32 :borders {}})
+----

src/img/vstval2reg.edn

@@ -0,0 +1,14 @@
+[bytefield]
+----
+(defattrs :plain [:plain {:font-family "M+ 1p Fallback" :font-size 24}])
+(def row-height 40)
+(def row-header-fn nil)
+(def left-margin 100)
+(def right-margin 100)
+(def boxes-per-row 32)
+(draw-column-headers {:height 20 :font-size 18 :labels (reverse ["0" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "VSXLEN-1"])})
+
+(draw-box "Addr"   {:span 32})
+
+(draw-box "VSXLEN" {:span 32 :borders {}})
+----

src/img/vstvalreg.edn

@@ -0,0 +1,20 @@
+[bytefield]
+----
+(defattrs :plain [:plain {:font-family "M+ 1p Fallback" :font-size 24}])
+(def row-height 40)
+(def row-header-fn nil)
+(def left-margin 100)
+(def right-margin 100)
+(def boxes-per-row 32)
+(draw-column-headers {:height 20 :font-size 18 :labels (reverse ["0" "" "" "3" "4" "" "" "" "" "" "" "" "" "" "" "15" "16" "" "" "19" "20" "" "" "" "" "" "" "" "" "" "" "VSXLEN-1"])})
+
+(draw-box "Reserved"   {:span 12})
+(draw-box "TYPE"       {:span 4})
+(draw-box "Reserved"   {:span 12})
+(draw-box "CAUSE"      {:span 4})
+
+(draw-box "VSXLEN-20" {:span 12 :borders {}})
+(draw-box "4"         {:span 4 :borders {}})
+(draw-box "12"        {:span 12 :borders {}})
+(draw-box "4"         {:span 4 :borders {}})
+----

src/riscv-integration.adoc

@@ -791,6 +791,24 @@ CHERI violations have the following order in priority:
 . Invalid address violation
 . Bounds violation (_Lowest_)
 
+[#mtval2,reftext="mtval2"]
+==== Machine Trap Value Register 2 (mtval2)
+
+The <<mtval2>> register is an MXLEN-bit read-write register, which is added as part of the
+Hypervisor extension. {cheri_base_ext_name} also requires the implementation of this CSR.
+
+When a CHERI fault is taken on any data memory access into into M-mode, <<mtval2>> is written
+with the MXLEN-bit effective address which caused the fault. This follows the existing rules for reporting
+load/store addresses to <<mtval>> from cite:[riscv-priv-spec].
+
+<<mtval2>> is set to zero for all other CHERI exceptions, and follows the standard rules for non-CHERI exceptions.
+
+If <<mtval>> is read-only-zero then <<mtval2>> is also read-only-zero.
+
+.Machine trap value register 2
+[#mtval2-format]
+include::img/mtval2reg.edn[]
+
 [#supervisor-level-csrs-section]
 === Supervisor-Level CSRs
 
@@ -993,10 +1011,25 @@ xref:stval-format[xrefstyle=short] to assist software in handling the trap.
 [#stval-format]
 include::img/stvalreg.edn[]
 
-TYPE is a CHERI-specific fault type that caused the exception while CAUSE
-is the cause of the fault. The possible CHERI types and causes are encoded as
-shown in xref:mtval-cheri-type[xrefstyle=short] and
-xref:mtval-cheri-causes[xrefstyle=short] respectively.
+The fields are identical to <<mtval>> for CHERI exceptions.
+
+[#stval2,reftext="stval2"]
+==== Supervisor Trap Value Register 2 (stval2)
+
+The <<stval2>> register is an SXLEN-bit read-write register.
+
+The CSR address is 0x24b.
+
+When a fault is taken into S-mode <<stval2>> is updated as for <<mtval2>> for all CHERI exceptions.
+It is set to zero in all other cases.
+
+NOTE: This is not a standard RISC-V CSR, but <<mtval2>> is. 0x14b is the regular location for the CSR.
+
+<<stval2>> holds the same set of values that <<mtval2>> can hold.
+
+.Supervisor trap value register 2
+[#stval2-format]
+include::img/stval2reg.edn[]
 
 === Unprivileged CSRs