[PATCH v2 05/12] um: compress memory related stub syscalls while adding them

benjamin
2024-04-29T13:48:34Z

To keep the number of syscalls that the stub has to do lower, compress
two consecutive syscalls of the same type if the second is just a
continuation of the first.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
---
arch/um/os-Linux/skas/mem.c | 39 +++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)

diff --git a/arch/um/os-Linux/skas/mem.c b/arch/um/os-Linux/skas/mem.c
index 03c8cde0b89b..e3128e080365 100644
--- a/arch/um/os-Linux/skas/mem.c
+++ b/arch/um/os-Linux/skas/mem.c
@@ -152,12 +152,37 @@ struct stub_syscall *syscall_stub_alloc(struct mm_id *mm_idp)
return sc;
}

+static struct stub_syscall *syscall_stub_get_previous(struct mm_id *mm_idp,
+ int syscall_type,
+ unsigned long virt)
+{
+ if (mm_idp->syscall_data_len > 0) {
+ struct stub_data *proc_data = (void *) mm_idp->stack;
+ struct stub_syscall *sc;
+
+ sc = &proc_data->syscall_data[mm_idp->syscall_data_len - 1];
+
+ if (sc->syscall == syscall_type &&
+ sc->mem.addr + sc->mem.length == virt)
+ return sc;
+ }
+
+ return NULL;
+}

void map(struct mm_id *mm_idp, unsigned long virt, unsigned long len, int prot,
int phys_fd, unsigned long long offset)
{
struct stub_syscall *sc;

+ /* Compress with previous syscall if that is possible */
+ sc = syscall_stub_get_previous(mm_idp, STUB_SYSCALL_MMAP, virt);
+ if (sc && sc->mem.prot == prot && sc->mem.fd == phys_fd &&
+ sc->mem.offset == MMAP_OFFSET(offset - sc->mem.length)) {
+ sc->mem.length += len;
+ return;
+ }
+
sc = syscall_stub_alloc(mm_idp);
sc->syscall = STUB_SYSCALL_MMAP;
sc->mem.addr = virt;
@@ -171,6 +196,13 @@ void unmap(struct mm_id *mm_idp, unsigned long addr, unsigned long len)
{
struct stub_syscall *sc;

+ /* Compress with previous syscall if that is possible */
+ sc = syscall_stub_get_previous(mm_idp, STUB_SYSCALL_MUNMAP, addr);
+ if (sc) {
+ sc->mem.length += len;
+ return;
+ }
+
sc = syscall_stub_alloc(mm_idp);
sc->syscall = STUB_SYSCALL_MUNMAP;
sc->mem.addr = addr;
@@ -182,6 +214,13 @@ void protect(struct mm_id *mm_idp, unsigned long addr, unsigned long len,
{
struct stub_syscall *sc;

+ /* Compress with previous syscall if that is possible */
+ sc = syscall_stub_get_previous(mm_idp, STUB_SYSCALL_MPROTECT, addr);
+ if (sc && sc->mem.prot == prot) {
+ sc->mem.length += len;
+ return;
+ }
+
sc = syscall_stub_alloc(mm_idp);
sc->syscall = STUB_SYSCALL_MPROTECT;
sc->mem.addr = addr;
--
2.44.0