[SeaBIOS] [PATCH 2/2] malloc: Fallback to low-zone when alloc from high-zone fails

[Liran Alon]

When 32-bit code needs to allocate memory which remains permanent
after completion of the initialization phase, it doesn't care if
it is allocated from high-zone or low-zone.

Currently all these cases just attempt to allocate from high-zone
as low-zone memory is scarce.

However, in cases we don't have enough space left in high-zone,
it makes sense to use low-zone as a fallback.

This commit fixes an issue of a VM which failed to boot when
configured with 16 PVSCSI disk controllers. The VM failed to boot
because pvscsi_init_rings() failed to allocate ring_dsc when
high-zone didn't had enough space for it.

Reviewed-by: Mark Kanda 
Signed-off-by: Liran Alon 
---
 src/malloc.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/malloc.h b/src/malloc.h
index 960a7f8000f8..d8bf5092dce0 100644
--- a/src/malloc.h
+++ b/src/malloc.h
@@ -31,7 +31,10 @@ static inline void *malloc_low(u32 size) {
     return _malloc(&ZoneLow, size, MALLOC_MIN_ALIGN);
 }
 static inline void *malloc_high(u32 size) {
-    return _malloc(&ZoneHigh, size, MALLOC_MIN_ALIGN);
+    void *ret = _malloc(&ZoneHigh, size, MALLOC_MIN_ALIGN);
+    if (ret)
+        return ret;
+    return malloc_low(size);
 }
 static inline void *malloc_fseg(u32 size) {
     return _malloc(&ZoneFSeg, size, MALLOC_MIN_ALIGN);
@@ -52,7 +55,10 @@ static inline void *memalign_low(u32 align, u32 size) {
     return _malloc(&ZoneLow, size, align);
 }
 static inline void *memalign_high(u32 align, u32 size) {
-    return _malloc(&ZoneHigh, size, align);
+    void *ret = _malloc(&ZoneHigh, size, align);
+    if (ret)
+        return ret;
+    return memalign_low(align, size);
 }
 static inline void *memalign_tmplow(u32 align, u32 size) {
     return _malloc(&ZoneTmpLow, size, align);