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Commit 2517617e authored by Michael Neuling's avatar Michael Neuling Committed by Benjamin Herrenschmidt
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powerpc: Fix context switch DSCR on POWER8 



POWER8 allows the DSCR to be accessed directly from userspace via a new SPR
number 0x3 (Rather than 0x11.  DSCR SPR number 0x11 is still used on POWER8 but
like POWER7, is only accessible in HV and OS modes).  Currently, we allow this
by setting H/FSCR DSCR bit on boot.

Unfortunately this doesn't work, as the kernel needs to see the DSCR change so
that it knows to no longer restore the system wide version of DSCR on context
switch (ie. to set thread.dscr_inherit).

This clears the H/FSCR DSCR bit initially.  If a process then accesses the DSCR
(via SPR 0x3), it'll trap into the kernel where we set thread.dscr_inherit in
facility_unavailable_exception().

We also change _switch() so that we set or clear the H/FSCR DSCR bit based on
the thread.dscr_inherit.

Signed-off-by: default avatarMichael Neuling <mikey@neuling.org>
Cc: <stable@vger.kernel.org> [v3.10]
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 74e400ce

arch/powerpc/kernel/entry_64.S

+26 −1
Original line number Diff line number Diff line
@@ -584,9 +584,34 @@ BEGIN_FTR_SECTION 
	ld	r7,DSCR_DEFAULT@toc(2)

	ld	r0,THREAD_DSCR(r4)

	cmpwi	r6,0

	li	r8, FSCR_DSCR

	bne	1f

	ld	r0,0(r7)

1:	cmpd	r0,r25

	b	3f

1:

  BEGIN_FTR_SECTION_NESTED(70)

	mfspr	r6, SPRN_FSCR

	or	r6, r6, r8

	mtspr	SPRN_FSCR, r6

    BEGIN_FTR_SECTION_NESTED(69)

	mfspr	r6, SPRN_HFSCR

	or	r6, r6, r8

	mtspr	SPRN_HFSCR, r6

    END_FTR_SECTION_NESTED(CPU_FTR_HVMODE, CPU_FTR_HVMODE, 69)

	b	4f

  END_FTR_SECTION_NESTED(CPU_FTR_ARCH_207S, CPU_FTR_ARCH_207S, 70)

3:

  BEGIN_FTR_SECTION_NESTED(70)

	mfspr	r6, SPRN_FSCR

	andc	r6, r6, r8

	mtspr	SPRN_FSCR, r6

    BEGIN_FTR_SECTION_NESTED(69)

	mfspr	r6, SPRN_HFSCR

	andc	r6, r6, r8

	mtspr	SPRN_HFSCR, r6

    END_FTR_SECTION_NESTED(CPU_FTR_HVMODE, CPU_FTR_HVMODE, 69)

  END_FTR_SECTION_NESTED(CPU_FTR_ARCH_207S, CPU_FTR_ARCH_207S, 70)

4:	cmpd	r0,r25

	beq	2f

	mtspr	SPRN_DSCR,r0

2:

arch/powerpc/kernel/traps.c

+34 −24
Original line number Diff line number Diff line
@@ -44,9 +44,7 @@ 
#include <asm/machdep.h>

#include <asm/rtas.h>

#include <asm/pmc.h>

#ifdef CONFIG_PPC32

#include <asm/reg.h>

#endif

#ifdef CONFIG_PMAC_BACKLIGHT

#include <asm/backlight.h>

#endif
@@ -1296,43 +1294,54 @@ void vsx_unavailable_exception(struct pt_regs *regs) 
	die("Unrecoverable VSX Unavailable Exception", regs, SIGABRT);

}



#ifdef CONFIG_PPC64

void facility_unavailable_exception(struct pt_regs *regs)

{

	static char *facility_strings[] = {

		"FPU",

		"VMX/VSX",

		"DSCR",

		"PMU SPRs",

		"BHRB",

		"TM",

		"AT",

		"EBB",

		"TAR",

		[FSCR_FP_LG] = "FPU",

		[FSCR_VECVSX_LG] = "VMX/VSX",

		[FSCR_DSCR_LG] = "DSCR",

		[FSCR_PM_LG] = "PMU SPRs",

		[FSCR_BHRB_LG] = "BHRB",

		[FSCR_TM_LG] = "TM",

		[FSCR_EBB_LG] = "EBB",

		[FSCR_TAR_LG] = "TAR",

	};

	char *facility, *prefix;

	char *facility = "unknown";

	u64 value;

	u8 status;

	bool hv;



	if (regs->trap == 0xf60) {

		value = mfspr(SPRN_FSCR);

		prefix = "";

	} else {

	hv = (regs->trap == 0xf80);

	if (hv)

		value = mfspr(SPRN_HFSCR);

		prefix = "Hypervisor ";

	else

		value = mfspr(SPRN_FSCR);



	status = value >> 56;

	if (status == FSCR_DSCR_LG) {

		/* User is acessing the DSCR.  Set the inherit bit and allow

		 * the user to set it directly in future by setting via the

		 * H/FSCR DSCR bit.

		 */

		current->thread.dscr_inherit = 1;

		if (hv)

			mtspr(SPRN_HFSCR, value | HFSCR_DSCR);

		else

			mtspr(SPRN_FSCR,  value | FSCR_DSCR);

		return;

	}



	value = value >> 56;

	if ((status < ARRAY_SIZE(facility_strings)) &&

	    facility_strings[status])

		facility = facility_strings[status];



	/* We restore the interrupt state now */

	if (!arch_irq_disabled_regs(regs))

		local_irq_enable();



	if (value < ARRAY_SIZE(facility_strings))

		facility = facility_strings[value];

	else

		facility = "unknown";



	pr_err("%sFacility '%s' unavailable, exception at 0x%lx, MSR=%lx\n",

		prefix, facility, regs->nip, regs->msr);

	       hv ? "Hypervisor " : "", facility, regs->nip, regs->msr);



	if (user_mode(regs)) {

		_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
@@ -1341,6 +1350,7 @@ void facility_unavailable_exception(struct pt_regs *regs) 


	die("Unexpected facility unavailable exception", regs, SIGABRT);

}

#endif



#ifdef CONFIG_PPC_TRANSACTIONAL_MEM