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diff --git a/usr.sbin/bhyve/e820.h b/usr.sbin/bhyve/e820.h
--- a/usr.sbin/bhyve/e820.h
+++ b/usr.sbin/bhyve/e820.h
@@ -18,11 +18,27 @@
E820_TYPE_NVS = 4
};
+enum e820_allocation_strategy {
+ /* allocate any address */
+ E820_ALLOCATE_ANY,
+ /* allocate lowest address larger than address */
+ E820_ALLOCATE_LOWEST,
+ /* allocate highest address lower than address */
+ E820_ALLOCATE_HIGHEST,
+ /* allocate a specific address */
+ E820_ALLOCATE_SPECIFIC
+};
+
struct e820_entry {
uint64_t base;
uint64_t length;
uint32_t type;
} __packed;
+#define E820_ALIGNMENT_NONE 1
+
+uint64_t e820_alloc(const uint64_t address, const uint64_t length,
+ const uint64_t alignment, const enum e820_memory_type type,
+ const enum e820_allocation_strategy strategy);
struct qemu_fwcfg_item *e820_get_fwcfg_item(void);
int e820_init(struct vmctx *const ctx);
diff --git a/usr.sbin/bhyve/e820.c b/usr.sbin/bhyve/e820.c
--- a/usr.sbin/bhyve/e820.c
+++ b/usr.sbin/bhyve/e820.c
@@ -20,6 +20,14 @@
#include "e820.h"
#include "qemu_fwcfg.h"
+/*
+ * E820 always uses 64 bit entries. Emulation code will use vm_paddr_t since it
+ * works on physical addresses. If vm_paddr_t is larger than uint64_t E820 can't
+ * hold all possible physical addresses and we can get into trouble.
+ */
+static_assert(sizeof(vm_paddr_t) <= sizeof(uint64_t),
+ "Unable to represent physical memory by E820 table");
+
#define E820_FWCFG_FILE_NAME "etc/e820"
#define KB (1024UL)
@@ -282,6 +290,102 @@
return (0);
}
+static uint64_t
+e820_alloc_highest(const uint64_t max_address, const uint64_t length,
+ const uint64_t alignment, const enum e820_memory_type type)
+{
+ struct e820_element *element;
+
+ TAILQ_FOREACH_REVERSE(element, &e820_table, e820_table, chain) {
+ uint64_t address, base, end;
+
+ end = MIN(max_address, element->end);
+ base = roundup2(element->base, alignment);
+
+ /*
+ * If end - length == 0, we would allocate memory at address 0. This
+ * address is mostly unusable and we should avoid allocating it.
+ * Therefore, search for another block in that case.
+ */
+ if (element->type != E820_TYPE_MEMORY || end < base ||
+ end - base < length || end - length == 0) {
+ continue;
+ }
+
+ address = rounddown2(end - length, alignment);
+
+ if (e820_add_entry(address, address + length, type) != 0) {
+ return (0);
+ }
+
+ return (address);
+ }
+
+ return (0);
+}
+
+static uint64_t
+e820_alloc_lowest(const uint64_t min_address, const uint64_t length,
+ const uint64_t alignment, const enum e820_memory_type type)
+{
+ struct e820_element *element;
+
+ TAILQ_FOREACH(element, &e820_table, chain) {
+ uint64_t base, end;
+
+ end = element->end;
+ base = MAX(min_address, roundup2(element->base, alignment));
+
+ /*
+ * If base == 0, we would allocate memory at address 0. This
+ * address is mostly unusable and we should avoid allocating it.
+ * Therefore, search for another block in that case.
+ */
+ if (element->type != E820_TYPE_MEMORY || end < base ||
+ end - base < length || base == 0) {
+ continue;
+ }
+
+ if (e820_add_entry(base, base + length, type) != 0) {
+ return (0);
+ }
+
+ return (base);
+ }
+
+ return (0);
+}
+
+uint64_t
+e820_alloc(const uint64_t address, const uint64_t length,
+ const uint64_t alignment, const enum e820_memory_type type,
+ const enum e820_allocation_strategy strategy)
+{
+ assert(powerof2(alignment));
+ assert((address & (alignment - 1)) == 0);
+
+ switch (strategy) {
+ case E820_ALLOCATE_ANY:
+ /*
+ * Allocate any address. Therefore, ignore the address parameter
+ * and reuse the code path for allocating the lowest address.
+ */
+ return (e820_alloc_lowest(0, length, alignment, type));
+ case E820_ALLOCATE_LOWEST:
+ return (e820_alloc_lowest(address, length, alignment, type));
+ case E820_ALLOCATE_HIGHEST:
+ return (e820_alloc_highest(address, length, alignment, type));
+ case E820_ALLOCATE_SPECIFIC:
+ if (e820_add_entry(address, address + length, type) != 0) {
+ return (0);
+ }
+
+ return (address);
+ }
+
+ return (0);
+}
+
int
e820_init(struct vmctx *const ctx)
{

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