Was requested by Jarkko:
https://lore.kernel.org/lkml/CYU504RLY7QU.QZY9LWC076NX@suppilovahvero/#t
[...]
Ah I missed that. No problem to me.
--- /dev/null
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _SGX_EPC_CGROUP_H_
+#define _SGX_EPC_CGROUP_H_
+
+#include <asm/sgx.h>
I don't see why you need <asm/sgx.h> here. Also, ...
+#include <linux/cgroup.h>
+#include <linux/misc_cgroup.h>
+
+#include "sgx.h"
... "sgx.h" already includes <asm/sgx.h>
[...]
right
+static inline struct sgx_cgroup *sgx_get_current_cg(void)
+{
+ /* get_current_misc_cg() never returns NULL when Kconfig enabled */
+ return sgx_cgroup_from_misc_cg(get_current_misc_cg());
+}
I spent some time looking into this. And yes if I was reading code
correctly the get_current_misc_cg() should never return NULL when Kconfig
is on.
I typed my analysis below in [*]. And it would be helpful if any cgroup
expert can have a second eye on this.
[...]
Thanks for checking this and I did similar and agree with the
conclusion. I think this is confirmed also by Michal's description AFAICT:
"
The current implementation creates root css object (see cgroup_init(),
cgroup_ssid_enabled() check is after cgroup_init_subsys()).
I.e. it will look like all tasks are members of root cgroup wrt given
controller permanently and controller attribute files won't exist."
After looking I believe we can even disable MISC cgroup at runtime for a
particular cgroup (haven't actually verified on real machine, though):
# echo "-misc" > /sys/fs/cgroup/my_group/cgroup.subtree_control
And if you look at the MISC cgroup core code, many functions actually
handle a NULL css, e.g., misc_cg_try_charge():
int misc_cg_try_charge(enum misc_res_type type,
struct misc_cg *cg, u64 amount)
{
...
if (!(valid_type(type) && cg &&
READ_ONCE(misc_res_capacity[type])))
return -EINVAL;
...
}
That's why I am still a little bit worried about this. And it's better
to have cgroup expert(s) to confirm here.
Btw, AMD SEV doesn't need to worry because it doesn't dereference @css
but just pass it to MISC cgroup core functions like
misc_cg_try_charge(). But for SGX, we actually dereference it directly.
