Comment # 15 on bug 1201066 from Joey Lee

A f88814cc25 patch be introduced to v5.8 kernel to set flag to read only if
SetVariable not be supported by firmware:

commit f88814cc2578c121e6edef686365036db72af0ed         [v5.8-rc7~14]
Author: Ard Biesheuvel <ardb@kernel.org>
Date:   Wed Jul 8 13:01:57 2020 +0300

    efi/efivars: Expose RT service availability via efivars abstraction


fs/efivarfs/super.c     
static int efivarfs_fill_super(struct super_block *sb, struct fs_context *fc)
{
...
        if (!efivar_supports_writes())
                sb->s_flags |= SB_RDONLY;
...