There seems to have been a broken assumption in the fpu context
restoring code. It restores the context of the running process, without
guarantee that the current process is the one that will be scheduled.
This caused fpu saving for a different process to be triggered without
fpu hardware being enabled, causing an fpu exception in the kernel. This
practically only shows up with DEBUG_RACE on. Fix my thruby+me.
The fix
. is to only set the fpu-in-use-by-this-process flag in the
exception handler, and then take care of fpu restoring when
actually returning to userspace
And the patch
. translates fpu saving and restoring to c in arch_system.c,
getting rid of a juicy chunk of assembly
. makes osfxsr_feature private to arch_system.c
. removes most of the arch dependent code from do_sigsend
the kernel. They are not used atm, but having them in trunk allows them
to be easily used when needed. To set a breakpoint that triggers when
the variable foo is written to (the most common use case), one calls:
breakpoint_set(vir2phys((vir_bytes) &foo), 0,
BREAKPOINT_FLAG_MODE_GLOBAL |
BREAKPOINT_FLAG_RW_WRITE |
BREAKPOINT_FLAG_LEN_4);
It can later be disabled using:
breakpoint_set(vir2phys((vir_bytes) &foo), 0,
BREAKPOINT_FLAG_MODE_OFF);
There are some limitations:
- There are at most four breakpoints (hardware limit); the index of the
breakpoint (0-3) is specified as the second parameter of
breakpoint_set.
- The breakpoint exception in the kernel is not handled and causes a
panic; it would be reasonably easy to change this by inspecing DR6,
printing a message, disabling the breakpoint and continuing. However,
in my experience even just a panic can be very useful.
- Breakpoints can be set only in the part of the address space that is
in every page table. It is useful for the kernel, but to use this for
user processes would require saving and restoring the debug registers
as part of the context switch. Although the CPU provides support for
local breakpoints (I implemened this as BREAKPOINT_FLAG_LOCAL) they
only work if task switching is used.
- there are no tasks running, we don't need TASK_PRIVILEGE priviledge anymore
- as there is no ring 1 anymore, there is no need for level0() to call sensitive
code from ring 1 in ring 0
- 286 related macros removed as clean up
- copies a mesage from/to userspace without need of translating
addresses
- the assumption is that the address space is installed, i.e. ldt and
cr3 are loaded correctly
- if a pagefault or a general protection occurs while copying from
userland to kernel (or vice versa) and error is returned which gives
the caller a chance to respond in a proper way
- error happens _only_ because of a wrong user pointer if the function
is used correctly
- if the prerequisites of the function do no hold, the function will
most likely fail as the user address becomes random
- the syscalls are pretty much just ipc calls, however, sendrec() is
used to implement system task (sys) calls
- sendrec() won't be used anymore for this, therefore ipc calls will
become pure ipc calls
- local APIC timer used as the source of time
- PIC is still used as the hw interrupt controller as we don't have
enough info without ACPI or MPS to set up IO APICs
- remapping of APIC when switching paging on, uses the new mechanism
to tell VM what phys areas to map in kernel's virtual space
- one more step to SMP
based on code by Arun C.
- after a trap to kernel, the code automatically switches to kernel
stack, in the future local to the CPU
- k_reenter variable replaced by a test whether the CS is kernel cs or
not. The information is passed further if needed. Removes a global
variable which would need to be cpu local
- no need for global variables describing the exception or trap
context. This information is kept on stack and a pointer to this
structure is passed to the C code as a single structure
- removed loadedcr3 variable and its use replaced by reading the %cr3
register
- no need to redisable interrupts in restart() as they are already
disabled.
- unified handling of traps that push and don't push errorcode
- removed save() function as the process context is not saved directly
to process table but saved as required by the trap code. Essentially
it means that save() code is inlined everywhere not only in the
exception handling routine
- returning from syscall is more arch independent - it sets the retger
in C
- top of the x86 stack contains the current CPU id and pointer to the
currently scheduled process (the one right interrupted) so the mode
switch code can find where to save the context without need to use
proc_ptr which will be cpu local in the future and therefore
difficult to access in assembler and expensive to access in general
- some more clean up of level0 code. No need to read-back the argument
passed in
%eax from the proc structure. The mode switch code does not clobber
%the general registers and hence we can just call what is in %eax
- many assebly macros in sconst.h as they will be reused by the apic
assembly
debugging info on panic: decode segment selectors and descriptors, now moved
to arch-specific part, prototypes added; sanity checking in debug.h made
optional with vmassert().
be used concurrently. pass the function in eax instead; this gets rid
of the global variable. also execute the function directly if we're
already trapped into the kernel.
revert of u32_t endpoint_t to int (some code assumes endpoints are
negative for negative slot numbers).
- no longer have kernel have its own page table that is loaded
on every kernel entry (trap, interrupt, exception). the primary
purpose is to reduce the number of required reloads.
Result:
- kernel can only access memory of process that was running when
kernel was entered
- kernel must be mapped into every process page table, so traps to
kernel keep working
Problem:
- kernel must often access memory of arbitrary processes (e.g. send
arbitrary processes messages); this can't happen directly any more;
usually because that process' page table isn't loaded at all, sometimes
because that memory isn't mapped in at all, sometimes because it isn't
mapped in read-write.
So:
- kernel must be able to map in memory of any process, in its own
address space.
Implementation:
- VM and kernel share a range of memory in which addresses of
all page tables of all processes are available. This has two purposes:
. Kernel has to know what data to copy in order to map in a range
. Kernel has to know where to write the data in order to map it in
That last point is because kernel has to write in the currently loaded
page table.
- Processes and kernel are separated through segments; kernel segments
haven't changed.
- The kernel keeps the process whose page table is currently loaded
in 'ptproc.'
- If it wants to map in a range of memory, it writes the value of the
page directory entry for that range into the page directory entry
in the currently loaded map. There is a slot reserved for such
purposes. The kernel can then access this memory directly.
- In order to do this, its segment has been increased (and the
segments of processes start where it ends).
- In the pagefault handler, detect if the kernel is doing
'trappable' memory access (i.e. a pagefault isn't a fatal
error) and if so,
- set the saved instruction pointer to phys_copy_fault,
breaking out of phys_copy
- set the saved eax register to the address of the page
fault, both for sanity checking and for checking in
which of the two ranges that phys_copy was called
with the fault occured
- Some boot-time processes do not have their own page table,
and are mapped in with the kernel, and separated with
segments. The kernel detects this using HASPT. If such a
process has to be scheduled, any page table will work and
no page table switch is done.
Major changes in kernel are
- When accessing user processes memory, kernel no longer
explicitly checks before it does so if that memory is OK.
It simply makes the mapping (if necessary), tries to do the
operation, and traps the pagefault if that memory isn't present;
if that happens, the copy function returns EFAULT.
So all of the CHECKRANGE_OR_SUSPEND macros are gone.
- Kernel no longer has to copy/read and parse page tables.
- A message copying optimisation: when messages are copied, and
the recipient isn't mapped in, they are copied into a buffer
in the kernel. This is done in QueueMess. The next time
the recipient is scheduled, this message is copied into
its memory. This happens in schedcheck().
This eliminates the mapping/copying step for messages, and makes
it easier to deliver messages. This eliminates soft_notify.
- Kernel no longer creates a page table at all, so the vm_setbuf
and pagetable writing in memory.c is gone.
Minor changes in kernel are
- ipc_stats thrown out, wasn't used
- misc flags all renamed to MF_*
- NOREC_* macros to enter and leave functions that should not
be called recursively; just sanity checks really
- code to fully decode segment selectors and descriptors
to print on exceptions
- lots of vmassert()s added, only executed if DEBUG_VMASSERT is 1
This is a backport form the SMP branch. Not required here, it only makes life
for SMP easier. And future merging too.
- filling the IDT is removed from prot_init()
- struct gate_table_s is a public type
- gate_table_pic is a global array as it is used by APIC code too
- idt_copy_vectors() is also global and used by idt_init() as well as
apic_idt_init()
- idt_init() is called right after prot_init() in system_init()
mainly in the kernel and headers. This split based on work by
Ingmar Alting <iaalting@cs.vu.nl> done for his Minix PowerPC architecture
port.
. kernel does not program the interrupt controller directly, do any
other architecture-dependent operations, or contain assembly any more,
but uses architecture-dependent functions in arch/$(ARCH)/.
. architecture-dependent constants and types defined in arch/$(ARCH)/include.
. <ibm/portio.h> moved to <minix/portio.h>, as they have become, for now,
architecture-independent functions.
. int86, sdevio, readbios, and iopenable are now i386-specific kernel calls
and live in arch/i386/do_* now.
. i386 arch now supports even less 86 code; e.g. mpx86.s and klib86.s have
gone, and 'machine.protected' is gone (and always taken to be 1 in i386).
If 86 support is to return, it should be a new architecture.
. prototypes for the architecture-dependent functions defined in
kernel/arch/$(ARCH)/*.c but used in kernel/ are in kernel/proto.h
. /etc/make.conf included in makefiles and shell scripts that need to
know the building architecture; it defines ARCH=<arch>, currently only
i386.
. some basic per-architecture build support outside of the kernel (lib)
. in clock.c, only dequeue a process if it was ready
. fixes for new include files
files deleted:
. mpx/klib.s - only for choosing between mpx/klib86 and -386
. klib86.s - only for 86
i386-specific files files moved (or arch-dependent stuff moved) to arch/i386/:
. mpx386.s (entry point)
. klib386.s
. sconst.h
. exception.c
. protect.c
. protect.h
. i8269.c
