Commit fbfe9c84 authored by Ingo van Lil's avatar Ingo van Lil Committed by Linus Torvalds
Browse files

um: Save FPU registers between task switches 



Some time ago Jeff prepared 42daba31 ("uml: stop saving process FP
state") for UML to stop saving the process FP state between task
switches.  The assumption was that since with SKAS0 every guest process
runs inside a host process context the host OS will take care of keeping
the proper FP state.

Unfortunately this is not true for multi-threaded applications, where
all guest threads share a single host process context yet all may use
the FPU on their own.  Although I haven't verified it I suspect things
to be even worse in SKAS3 mode where all guest processes run inside a
single host process.

The patch reintroduces the saving and restoring of the FP context
between task switches.

[richard@nod.at: Ingo posted this patch in 2009, sadly it was never applied
and got lost. Now in 2011 the problem was reported by Gunnar.]

Signed-off-by: default avatarIngo van Lil <inguin@gmx.de>
Signed-off-by: default avatarRichard Weinberger <richard@nod.at>
Reported-by: default avatar <gunnarlindroth@hotmail.com>
Tested-by: default avatar <gunnarlindroth@hotmail.com>
Cc: Stanislav Meduna <stano@meduna.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b40997b8

arch/um/include/shared/registers.h

+1 −1
Original line number Diff line number Diff line
@@ -16,7 +16,7 @@ extern int restore_fpx_registers(int pid, unsigned long *fp_regs); 
extern int save_registers(int pid, struct uml_pt_regs *regs);

extern int restore_registers(int pid, struct uml_pt_regs *regs);

extern int init_registers(int pid);

extern void get_safe_registers(unsigned long *regs);

extern void get_safe_registers(unsigned long *regs, unsigned long *fp_regs);

extern unsigned long get_thread_reg(int reg, jmp_buf *buf);

extern int get_fp_registers(int pid, unsigned long *regs);

extern int put_fp_registers(int pid, unsigned long *regs);

arch/um/kernel/process.c

+1 −1
Original line number Diff line number Diff line
@@ -202,7 +202,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, 
		arch_copy_thread(&current->thread.arch, &p->thread.arch);

	}

	else {

		get_safe_registers(p->thread.regs.regs.gp);

		get_safe_registers(p->thread.regs.regs.gp, p->thread.regs.regs.fp);

		p->thread.request.u.thread = current->thread.request.u.thread;

		handler = new_thread_handler;

	}

arch/um/os-Linux/registers.c

+8 −1
Original line number Diff line number Diff line
@@ -8,6 +8,8 @@ 
#include <string.h>

#include <sys/ptrace.h>

#include "sysdep/ptrace.h"

#include "sysdep/ptrace_user.h"

#include "registers.h"



int save_registers(int pid, struct uml_pt_regs *regs)

{
@@ -32,6 +34,7 @@ int restore_registers(int pid, struct uml_pt_regs *regs) 
/* This is set once at boot time and not changed thereafter */



static unsigned long exec_regs[MAX_REG_NR];

static unsigned long exec_fp_regs[FP_SIZE];



int init_registers(int pid)

{
@@ -42,10 +45,14 @@ int init_registers(int pid) 
		return -errno;



	arch_init_registers(pid);

	get_fp_registers(pid, exec_fp_regs);

	return 0;

}



void get_safe_registers(unsigned long *regs)

void get_safe_registers(unsigned long *regs, unsigned long *fp_regs)

{

	memcpy(regs, exec_regs, sizeof(exec_regs));



	if (fp_regs)

		memcpy(fp_regs, exec_fp_regs, sizeof(exec_fp_regs));

}

arch/um/os-Linux/skas/mem.c

+1 −1
Original line number Diff line number Diff line
@@ -39,7 +39,7 @@ static unsigned long syscall_regs[MAX_REG_NR]; 


static int __init init_syscall_regs(void)

{

	get_safe_registers(syscall_regs);

	get_safe_registers(syscall_regs, NULL);

	syscall_regs[REGS_IP_INDEX] = STUB_CODE +

		((unsigned long) &batch_syscall_stub -

		 (unsigned long) &__syscall_stub_start);

arch/um/os-Linux/skas/process.c

+18 −1
Original line number Diff line number Diff line
@@ -373,6 +373,9 @@ void userspace(struct uml_pt_regs *regs) 
		if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp))

			fatal_sigsegv();



		if (put_fp_registers(pid, regs->fp))

			fatal_sigsegv();



		/* Now we set local_using_sysemu to be used for one loop */

		local_using_sysemu = get_using_sysemu();
@@ -399,6 +402,12 @@ void userspace(struct uml_pt_regs *regs) 
			fatal_sigsegv();

		}



		if (get_fp_registers(pid, regs->fp)) {

			printk(UM_KERN_ERR "userspace -  get_fp_registers failed, "

			       "errno = %d\n", errno);

			fatal_sigsegv();

		}



		UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */



		if (WIFSTOPPED(status)) {
@@ -457,10 +466,11 @@ void userspace(struct uml_pt_regs *regs) 
}



static unsigned long thread_regs[MAX_REG_NR];

static unsigned long thread_fp_regs[FP_SIZE];



static int __init init_thread_regs(void)

{

	get_safe_registers(thread_regs);

	get_safe_registers(thread_regs, thread_fp_regs);

	/* Set parent's instruction pointer to start of clone-stub */

	thread_regs[REGS_IP_INDEX] = STUB_CODE +

				(unsigned long) stub_clone_handler -
@@ -503,6 +513,13 @@ int copy_context_skas0(unsigned long new_stack, int pid) 
		return err;

	}



	err = put_fp_registers(pid, thread_fp_regs);

	if (err < 0) {

		printk(UM_KERN_ERR "copy_context_skas0 : put_fp_registers "

		       "failed, pid = %d, err = %d\n", pid, err);

		return err;

	}



	/* set a well known return code for detection of child write failure */

	child_data->err = 12345678;

CRA Git | Maintained and supported by SUSTech CRA and CCSE