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s390/kvm: avoid global config of vm.alloc_pgste=1 

The system control vm.alloc_pgste is used to control the size of the
page tables, either 2K or 4K. The idea is that a KVM host sets the
vm.alloc_pgste control to 1 which causes *all* new processes to run
with 4K page tables. For a non-kvm system the control should stay off
to save on memory used for page tables.

Trouble is that distributions choose to set the control globally to
be able to run KVM guests. This wastes memory on non-KVM systems.

Introduce the PT_S390_PGSTE ELF segment type to "mark" the qemu
executable with it. All executables with this (empty) segment in
its ELF phdr array will be started with 4K page tables. Any executable
without PT_S390_PGSTE will run with the default 2K page tables.

This removes the need to set vm.alloc_pgste=1 for a KVM host and
minimizes the waste of memory for page tables.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2017-06-07 14:10:24 +02:00
parent a752598254
commit 23fefe119c
6 changed files with 53 additions and 2 deletions
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1
arch/s390/Kconfig
View File

@ -64,6 +64,7 @@ config ARCH_SUPPORTS_UPROBES
config S390
def_bool y
select ARCH_BINFMT_ELF_STATE
select ARCH_HAS_DEVMEM_IS_ALLOWED
select ARCH_HAS_ELF_RANDOMIZE
select ARCH_HAS_GCOV_PROFILE_ALL

32
arch/s390/include/asm/elf.h
View File

@ -117,6 +117,9 @@
#define ELF_DATA ELFDATA2MSB
#define ELF_ARCH EM_S390
/* s390 specific phdr types */
#define PT_S390_PGSTE 0x70000000
/*
* ELF register definitions..
*/
@ -151,6 +154,35 @@ extern unsigned int vdso_enabled;
&& (x)->e_ident[EI_CLASS] == ELF_CLASS)
#define compat_start_thread start_thread31
struct arch_elf_state {
int rc;
};
#define INIT_ARCH_ELF_STATE { .rc = 0 }
#define arch_check_elf(ehdr, interp, interp_ehdr, state) (0)
#ifdef CONFIG_PGSTE
#define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) \
({ \
struct arch_elf_state *_state = state; \
if ((phdr)->p_type == PT_S390_PGSTE && \
!page_table_allocate_pgste && \
!test_thread_flag(TIF_PGSTE) && \
!current->mm->context.alloc_pgste) { \
set_thread_flag(TIF_PGSTE); \
set_pt_regs_flag(task_pt_regs(current), \
PIF_SYSCALL_RESTART); \
_state->rc = -EAGAIN; \
} \
_state->rc; \
})
#else
#define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) \
({ \
(state)->rc; \
})
#endif
/* For SVR4/S390 the function pointer to be registered with `atexit` is
passed in R14. */
#define ELF_PLAT_INIT(_r, load_addr) \

4
arch/s390/include/asm/mmu_context.h
View File

@ -25,7 +25,9 @@ static inline int init_new_context(struct task_struct *tsk,
mm->context.gmap_asce = 0;
mm->context.flush_mm = 0;
#ifdef CONFIG_PGSTE
mm->context.alloc_pgste = page_table_allocate_pgste;
mm->context.alloc_pgste = page_table_allocate_pgste ||
test_thread_flag(TIF_PGSTE) ||
current->mm->context.alloc_pgste;
mm->context.has_pgste = 0;
mm->context.use_skey = 0;
mm->context.use_cmma = 0;

2
arch/s390/include/asm/ptrace.h
View File

@ -11,9 +11,11 @@
#define PIF_SYSCALL 0 /* inside a system call */
#define PIF_PER_TRAP 1 /* deliver sigtrap on return to user */
#define PIF_SYSCALL_RESTART 2 /* restart the current system call */
#define _PIF_SYSCALL _BITUL(PIF_SYSCALL)
#define _PIF_PER_TRAP _BITUL(PIF_PER_TRAP)
#define _PIF_SYSCALL_RESTART _BITUL(PIF_SYSCALL_RESTART)
#ifndef __ASSEMBLY__

1
arch/s390/include/asm/thread_info.h
View File

@ -58,6 +58,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
#define TIF_UPROBE 3 /* breakpointed or single-stepping */
#define TIF_GUARDED_STORAGE 4 /* load guarded storage control block */
#define TIF_PATCH_PENDING 5 /* pending live patching update */
#define TIF_PGSTE 6 /* New mm's will use 4K page tables */
#define TIF_31BIT 16 /* 32bit process */
#define TIF_MEMDIE 17 /* is terminating due to OOM killer */

15
arch/s390/kernel/entry.S
View File

@ -52,7 +52,7 @@ _TIF_TRACE = (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | \
_TIF_SYSCALL_TRACEPOINT)
_CIF_WORK = (_CIF_MCCK_PENDING | _CIF_ASCE_PRIMARY | \
_CIF_ASCE_SECONDARY | _CIF_FPU)
_PIF_WORK = (_PIF_PER_TRAP)
_PIF_WORK = (_PIF_PER_TRAP | _PIF_SYSCALL_RESTART)
#define BASED(name) name-cleanup_critical(%r13)
@ -334,6 +334,8 @@ ENTRY(system_call)
jo .Lsysc_mcck_pending
TSTMSK __TI_flags(%r12),_TIF_NEED_RESCHED
jo .Lsysc_reschedule
TSTMSK __PT_FLAGS(%r11),_PIF_SYSCALL_RESTART
jo .Lsysc_syscall_restart
#ifdef CONFIG_UPROBES
TSTMSK __TI_flags(%r12),_TIF_UPROBE
jo .Lsysc_uprobe_notify
@ -347,6 +349,8 @@ ENTRY(system_call)
jo .Lsysc_patch_pending # handle live patching just before
# signals and possible syscall restart
#endif
TSTMSK __PT_FLAGS(%r11),_PIF_SYSCALL_RESTART
jo .Lsysc_syscall_restart
TSTMSK __TI_flags(%r12),_TIF_SIGPENDING
jo .Lsysc_sigpending
TSTMSK __TI_flags(%r12),_TIF_NOTIFY_RESUME
@ -447,6 +451,15 @@ ENTRY(system_call)
larl %r14,.Lsysc_return
jg do_per_trap
#
# _PIF_SYSCALL_RESTART is set, repeat the current system call
#
.Lsysc_syscall_restart:
ni __PT_FLAGS+7(%r11),255-_PIF_SYSCALL_RESTART
lmg %r1,%r7,__PT_R1(%r11) # load svc arguments
lg %r2,__PT_ORIG_GPR2(%r11)
j .Lsysc_do_svc
#
# call tracehook_report_syscall_entry/tracehook_report_syscall_exit before
# and after the system call