Revert "MIPS: Save/restore MSA context around signals"

This reverts commit eec43a224cf1 "MIPS: Save/restore MSA context around
signals" and the MSA parts of ca750649e08c "MIPS: kernel: signal:
Prevent save/restore FPU context in user memory" (the restore path of
which appears incorrect anyway...).

The reverted patch took care not to break compatibility with userland
users of struct sigcontext, but inadvertantly changed the offset of the
uc_sigmask field of struct ucontext. Thus Linux v3.15 breaks the
userland ABI. The MSA context will need to be saved via some other
opt-in mechanism, but for now revert the change to reduce the fallout.

This will have minimal impact upon use of MSA since the only supported
CPU which includes it (the P5600) is 32-bit and therefore requires that
the experimental CONFIG_MIPS_O32_FP64_SUPPORT Kconfig option be selected
before the kernel will set FR=1 for a task, a requirement for MSA use.
Thus the users of MSA are limited to known small groups of people & this
patch won't be breaking any previously working MSA-using userland
outside of experimental settings.

[ralf@linux-mips.org: Fixed rejects.]

Cc: stable@vger.kernel.org
Reported-by: Joseph S. Myers <joseph@codesourcery.com>
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7107/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 8 insertions, 71 deletions

diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
index 33133d3df3e5..9e60d117e41e 100644
--- a/arch/mips/kernel/signal.c
+++ b/arch/mips/kernel/signal.c
@@ -31,7 +31,6 @@
 #include <linux/bitops.h>
 #include <asm/cacheflush.h>
 #include <asm/fpu.h>
-#include <asm/msa.h>
 #include <asm/sim.h>
 #include <asm/ucontext.h>
 #include <asm/cpu-features.h>
@@ -48,9 +47,6 @@ static int (*restore_fp_context)(struct sigcontext __user *sc);
 extern asmlinkage int _save_fp_context(struct sigcontext __user *sc);
 extern asmlinkage int _restore_fp_context(struct sigcontext __user *sc);
 
-extern asmlinkage int _save_msa_context(struct sigcontext __user *sc);
-extern asmlinkage int _restore_msa_context(struct sigcontext __user *sc);
-
 struct sigframe {
 	u32 sf_ass[4];		/* argument save space for o32 */
 	u32 sf_pad[2];		/* Was: signal trampoline */
@@ -100,60 +96,20 @@ static int copy_fp_from_sigcontext(struct sigcontext __user *sc)
 }
 
 /*
- * These functions will save only the upper 64 bits of the vector registers,
- * since the lower 64 bits have already been saved as the scalar FP context.
- */
-static int copy_msa_to_sigcontext(struct sigcontext __user *sc)
-{
-	int i;
-	int err = 0;
-
-	for (i = 0; i < NUM_FPU_REGS; i++) {
-		err |=
-		    __put_user(get_fpr64(&current->thread.fpu.fpr[i], 1),
-			       &sc->sc_msaregs[i]);
-	}
-	err |= __put_user(current->thread.fpu.msacsr, &sc->sc_msa_csr);
-
-	return err;
-}
-
-static int copy_msa_from_sigcontext(struct sigcontext __user *sc)
-{
-	int i;
-	int err = 0;
-	u64 val;
-
-	for (i = 0; i < NUM_FPU_REGS; i++) {
-		err |= __get_user(val, &sc->sc_msaregs[i]);
-		set_fpr64(&current->thread.fpu.fpr[i], 1, val);
-	}
-	err |= __get_user(current->thread.fpu.msacsr, &sc->sc_msa_csr);
-
-	return err;
-}
-
-/*
  * Helper routines
  */
-static int protected_save_fp_context(struct sigcontext __user *sc,
-				     unsigned used_math)
+static int protected_save_fp_context(struct sigcontext __user *sc)
 {
 	int err;
-	bool save_msa = cpu_has_msa && (used_math & USEDMATH_MSA);
 #ifndef CONFIG_EVA
 	while (1) {
 		lock_fpu_owner();
 		if (is_fpu_owner()) {
 			err = save_fp_context(sc);
-			if (save_msa && !err)
-				err = _save_msa_context(sc);
 			unlock_fpu_owner();
 		} else {
 			unlock_fpu_owner();
 			err = copy_fp_to_sigcontext(sc);
-			if (save_msa && !err)
-				err = copy_msa_to_sigcontext(sc);
 		}
 		if (likely(!err))
 			break;
@@ -169,38 +125,24 @@ static int protected_save_fp_context(struct sigcontext __user *sc,
 	 * EVA does not have FPU EVA instructions so saving fpu context directly
 	 * does not work.
 	 */
-	disable_msa();
 	lose_fpu(1);
 	err = save_fp_context(sc); /* this might fail */
-	if (save_msa && !err)
-		err = copy_msa_to_sigcontext(sc);
 #endif
 	return err;
 }
 
-static int protected_restore_fp_context(struct sigcontext __user *sc,
-					unsigned used_math)
+static int protected_restore_fp_context(struct sigcontext __user *sc)
 {
 	int err, tmp __maybe_unused;
-	bool restore_msa = cpu_has_msa && (used_math & USEDMATH_MSA);
 #ifndef CONFIG_EVA
 	while (1) {
 		lock_fpu_owner();
 		if (is_fpu_owner()) {
 			err = restore_fp_context(sc);
-			if (restore_msa && !err) {
-				enable_msa();
-				err = _restore_msa_context(sc);
-			} else {
-				/* signal handler may have used MSA */
-				disable_msa();
-			}
 			unlock_fpu_owner();
 		} else {
 			unlock_fpu_owner();
 			err = copy_fp_from_sigcontext(sc);
-			if (!err && (used_math & USEDMATH_MSA))
-				err = copy_msa_from_sigcontext(sc);
 		}
 		if (likely(!err))
 			break;
@@ -216,11 +158,8 @@ static int protected_restore_fp_context(struct sigcontext __user *sc,
 	 * EVA does not have FPU EVA instructions so restoring fpu context
 	 * directly does not work.
 	 */
-	enable_msa();
 	lose_fpu(0);
 	err = restore_fp_context(sc); /* this might fail */
-	if (restore_msa && !err)
-		err = copy_msa_from_sigcontext(sc);
 #endif
 	return err;
 }
@@ -252,8 +191,7 @@ int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
 		err |= __put_user(rddsp(DSP_MASK), &sc->sc_dsp);
 	}
 
-	used_math = used_math() ? USEDMATH_FP : 0;
-	used_math |= thread_msa_context_live() ? USEDMATH_MSA : 0;
+	used_math = !!used_math();
 	err |= __put_user(used_math, &sc->sc_used_math);
 
 	if (used_math) {
@@ -261,7 +199,7 @@ int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
 		 * Save FPU state to signal context. Signal handler
 		 * will "inherit" current FPU state.
 		 */
-		err |= protected_save_fp_context(sc, used_math);
+		err |= protected_save_fp_context(sc);
 	}
 	return err;
 }
@@ -286,14 +224,14 @@ int fpcsr_pending(unsigned int __user *fpcsr)
 }
 
 static int
-check_and_restore_fp_context(struct sigcontext __user *sc, unsigned used_math)
+check_and_restore_fp_context(struct sigcontext __user *sc)
 {
 	int err, sig;
 
 	err = sig = fpcsr_pending(&sc->sc_fpc_csr);
 	if (err > 0)
 		err = 0;
-	err |= protected_restore_fp_context(sc, used_math);
+	err |= protected_restore_fp_context(sc);
 	return err ?: sig;
 }
 
@@ -333,10 +271,9 @@ int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
 	if (used_math) {
 		/* restore fpu context if we have used it before */
 		if (!err)
-			err = check_and_restore_fp_context(sc, used_math);
+			err = check_and_restore_fp_context(sc);
 	} else {
-		/* signal handler may have used FPU or MSA. Disable them. */
-		disable_msa();
+		/* signal handler may have used FPU.  Give it up. */
 		lose_fpu(0);
 	}