um: Delay flushing syscalls until the thread is restarted

As running the syscalls is expensive due to context switches, we should
do so as late as possible in case more syscalls need to be queued later
on. This will also benefit a later move to a SECCOMP enabled userspace
as in that case the need for extra context switches is removed entirely.

Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net>
Link: https://patch.msgid.link/20240703134536.1161108-9-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

2 files changed, 10 insertions, 19 deletions

diff --git a/arch/um/kernel/skas/process.c b/arch/um/kernel/skas/process.c
index 99a5cbb36083..41901a74fccc 100644
--- a/arch/um/kernel/skas/process.c
+++ b/arch/um/kernel/skas/process.c
@@ -50,3 +50,11 @@ unsigned long current_stub_stack(void)
 
 	return current->mm->context.id.stack;
 }
+
+struct mm_id *current_mm_id(void)
+{
+	if (current->mm == NULL)
+		return NULL;
+
+	return &current->mm->context.id;
+}
diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c
index a89e2886485f..1eee7134cba8 100644
--- a/arch/um/kernel/tlb.c
+++ b/arch/um/kernel/tlb.c
@@ -53,7 +53,7 @@ struct host_vm_change {
 	   .index	= 0, \
 	   .force	= force })
 
-static void report_enomem(void)
+void report_enomem(void)
 {
 	printk(KERN_ERR "UML ran out of memory on the host side! "
 			"This can happen due to a memory limitation or "
@@ -338,15 +338,6 @@ static void fix_range_common(struct mm_struct *mm, unsigned long start_addr,
 
 	if (!ret)
 		ret = do_ops(&hvc, hvc.index, 1);
-
-	/* This is not an else because ret is modified above */
-	if (ret) {
-		struct mm_id *mm_idp = &current->mm->context.id;
-
-		printk(KERN_ERR "fix_range_common: failed, killing current "
-		       "process: %d\n", task_tgid_vnr(current));
-		mm_idp->kill = 1;
-	}
 }
 
 static int flush_tlb_kernel_range_common(unsigned long start, unsigned long end)
@@ -461,7 +452,7 @@ void flush_tlb_page(struct vm_area_struct *vma, unsigned long address)
 	pmd_t *pmd;
 	pte_t *pte;
 	struct mm_struct *mm = vma->vm_mm;
-	int r, w, x, prot, err = 0;
+	int r, w, x, prot;
 	struct mm_id *mm_id;
 
 	address &= PAGE_MASK;
@@ -509,14 +500,6 @@ void flush_tlb_page(struct vm_area_struct *vma, unsigned long address)
 	} else if (pte_newprot(*pte))
 		protect(mm_id, address, PAGE_SIZE, prot);
 
-	err = syscall_stub_flush(mm_id);
-	if (err) {
-		if (err == -ENOMEM)
-			report_enomem();
-
-		goto kill;
-	}
-
 	*pte = pte_mkuptodate(*pte);
 
 	return;