INT32
EFIAPI
TestAndClearBit (
IN INT32 Bit,
IN VOID *Address
)
{
UINT16 Word, Read;
UINT16 Mask;
//
// Calculate the effective address relative to 'Address' based on the
// higher order bits of 'Bit'. Use signed shift instead of division to
// ensure we round towards -Inf, and end up with a positive shift in
// 'Bit', even if 'Bit' itself is negative.
//
Address += (Bit >> 4) * sizeof(UINT16);
Mask = 1U << (Bit & 15);
for (Word = *(UINT16 *) Address; Word & Mask; Word = Read) {
Read = InterlockedCompareExchange16 (Address, Word, Word & ~Mask);
if (Read == Word) {
return 1;
}
}
return 0;
}
static NTSTATUS
GnttabRevokeForeignAccess(
IN PINTERFACE Interface,
IN PXENBUS_GNTTAB_CACHE Cache,
IN BOOLEAN Locked,
IN PXENBUS_GNTTAB_ENTRY Entry
)
{
PXENBUS_GNTTAB_CONTEXT Context = Interface->Context;
volatile SHORT *flags;
ULONG Attempt;
NTSTATUS status;
ASSERT3U(Entry->Magic, ==, XENBUS_GNTTAB_ENTRY_MAGIC);
ASSERT3U(Entry->Reference, >=, XENBUS_GNTTAB_RESERVED_ENTRY_COUNT);
ASSERT3U(Entry->Reference, <, (Context->FrameIndex + 1) * XENBUS_GNTTAB_ENTRY_PER_FRAME);
flags = (volatile SHORT *)&Context->Table[Entry->Reference].flags;
Attempt = 0;
while (Attempt++ < 100) {
uint16_t Old;
uint16_t New;
Old = *flags;
Old &= ~(GTF_reading | GTF_writing);
New = Old & ~GTF_permit_access;
if (InterlockedCompareExchange16(flags, New, Old) == Old)
break;
SchedYield();
}
status = STATUS_UNSUCCESSFUL;
if (Attempt == 100)
goto fail1;
RtlZeroMemory(&Context->Table[Entry->Reference],
sizeof (grant_entry_v1_t));
RtlZeroMemory(&Entry->Entry,
sizeof (grant_entry_v1_t));
XENBUS_CACHE(Put,
&Context->CacheInterface,
Cache->Cache,
Entry,
Locked);
return STATUS_SUCCESS;
fail1:
Error("fail1 (%08x)\n", status);
return status;
}
static NTSTATUS
GnttabRevokeForeignAccess(
IN PXENBUS_GNTTAB_CONTEXT Context,
IN PXENBUS_GNTTAB_CACHE Cache,
IN BOOLEAN Locked,
IN PXENBUS_GNTTAB_DESCRIPTOR Descriptor
)
{
grant_entry_v1_t *Entry;
volatile SHORT *Flags;
ULONG Attempt;
NTSTATUS status;
ASSERT3U(Descriptor->Magic, ==, GNTTAB_DESCRIPTOR_MAGIC);
ASSERT3U(Descriptor->Reference, >=, GNTTAB_RESERVED_ENTRY_COUNT);
ASSERT3U(Descriptor->Reference, <, (Context->FrameIndex + 1) * GNTTAB_ENTRY_PER_FRAME);
Entry = &Context->Entry[Descriptor->Reference];
Flags = (volatile SHORT *)&Entry->flags;
Attempt = 0;
while (Attempt++ < 100) {
uint16_t Old;
uint16_t New;
Old = *Flags;
Old &= ~(GTF_reading | GTF_writing);
New = Old & ~GTF_permit_access;
if (InterlockedCompareExchange16(Flags, New, Old) == Old)
break;
SchedYield();
}
status = STATUS_UNSUCCESSFUL;
if (Attempt == 100)
goto fail1;
RtlZeroMemory(Entry, sizeof (grant_entry_v1_t));
RtlZeroMemory(&Descriptor->Entry, sizeof (grant_entry_v1_t));
CACHE(Put,
Context->CacheInterface,
Cache->Cache,
Descriptor,
Locked);
return STATUS_SUCCESS;
fail1:
Error("fail1 (%08x)\n", status);
return status;
}
bool trySet(Type *p, Type newVal, Type oldVal)
{
bool success = false;
#if defined(X_MSVC)
xAssertIsSpecificAligned(p, 8);
// try to lock the updating flag, if we cant, someone else is working.
success = InterlockedCompareExchange16(p, newVal, oldVal) == oldVal;
#else
success = __sync_val_compare_and_swap(p, oldVal, newVal) == oldVal;
#endif
return success;
}
