| Message ID | 20221104172737.391978-4-ajd@linux.ibm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | VMAP_STACK support for book3s64 | expand |
Le 04/11/2022 à 18:27, Andrew Donnellan a écrit : > When we enter and return from an OPAL call, there's three pieces of state > we have to save and restore: the stack pointer, the PACA pointer, and the > MSR. However, there's only two registers that OPAL is guaranteed to > preserve for us (r1 for the stack pointer and r13 for the PACA), so the MSR > gets saved on the stack. > > This becomes problematic when we enable VMAP_STACK, as we need to re-enable > translation in order to access the virtually mapped stack... and to > re-enable translation, we need to restore the MSR. Do you need to restore MSR really ? Can't you just set MSR_DR to access the stack then restore MSR ? Or maybe you don't want to do it in two steps for performance reason ? > > Keep the MSR in r13, and instead store the PACA pointer on the stack - we > can restore the MSR first, then restore the PACA into r13. > > Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com> > --- > .../powerpc/platforms/powernv/opal-wrappers.S | 43 +++++++++++-------- > 1 file changed, 26 insertions(+), 17 deletions(-) > > diff --git a/arch/powerpc/platforms/powernv/opal-wrappers.S b/arch/powerpc/platforms/powernv/opal-wrappers.S > index 0ed95f753416..d692869ee0ce 100644 > --- a/arch/powerpc/platforms/powernv/opal-wrappers.S > +++ b/arch/powerpc/platforms/powernv/opal-wrappers.S > @@ -23,40 +23,49 @@ > _GLOBAL_TOC(__opal_call) > mflr r0 > std r0,PPC_LR_STKOFF(r1) > - ld r12,STK_PARAM(R12)(r1) > - li r0,MSR_IR|MSR_DR|MSR_LE > - andc r12,r12,r0 > LOAD_REG_ADDR(r11, opal_return) > mtlr r11 > LOAD_REG_ADDR(r11, opal) > ld r2,0(r11) > ld r11,8(r11) > mtspr SPRN_HSRR0,r11 > - mtspr SPRN_HSRR1,r12 > + > /* set token to r0 */ > ld r0,STK_PARAM(R11)(r1) > + > + /* > + * We need to keep the MSR value in a register that is preserved by > + * OPAL, so that we don't need to access the stack before we restore > + * the MSR, as the stack may be vmalloced and thus require MMU. > + * > + * Move the PACA from R13 into the stack red zone, and put MSR in R13. > + */ > + std r13,-8(r1) > + ld r13,STK_PARAM(R12)(r1) > + > + /* Switch off MMU, LE */ > + li r11,MSR_IR|MSR_DR|MSR_LE > + andc r11,r13,r11 > + > + mtspr SPRN_HSRR1,r11 > hrfid > opal_return: > /* > * Restore MSR on OPAL return. The MSR is set to big-endian. > */ > #ifdef __BIG_ENDIAN__ > - ld r11,STK_PARAM(R12)(r1) > - mtmsrd r11 > + mtmsrd r13 > #else > /* Endian can only be switched with rfi, must byte reverse MSR load */ > - .short 0x4039 /* li r10,STK_PARAM(R12) */ > - .byte (STK_PARAM(R12) >> 8) & 0xff > - .byte STK_PARAM(R12) & 0xff > - > - .long 0x280c6a7d /* ldbrx r11,r10,r1 */ > - .long 0x05009f42 /* bcl 20,31,$+4 */ > - .long 0xa602487d /* mflr r10 */ > - .long 0x14004a39 /* addi r10,r10,20 */ > - .long 0xa64b5a7d /* mthsrr0 r10 */ > - .long 0xa64b7b7d /* mthsrr1 r11 */ > - .long 0x2402004c /* hrfid */ > + .long 0x05009f42 /* bcl 20,31,$+4 (LR <- next insn addr) */ > + .long 0xa602487d /* mflr r10 */ > + .long 0x14004a39 /* addi r10,r10,20 (r10 <- addr after #endif) */ > + .long 0xa64b5a7d /* mthsrr0 r10 (new NIP) */ > + .long 0xa64bbb7d /* mthsrr1 r13 (new MSR) */ > + .long 0x2402004c /* hrfid */ > #endif > + /* Restore PACA */ > + ld r13,-8(r1) > LOAD_PACA_TOC() > ld r0,PPC_LR_STKOFF(r1) > mtlr r0
diff --git a/arch/powerpc/platforms/powernv/opal-wrappers.S b/arch/powerpc/platforms/powernv/opal-wrappers.S index 0ed95f753416..d692869ee0ce 100644 --- a/arch/powerpc/platforms/powernv/opal-wrappers.S +++ b/arch/powerpc/platforms/powernv/opal-wrappers.S @@ -23,40 +23,49 @@ _GLOBAL_TOC(__opal_call) mflr r0 std r0,PPC_LR_STKOFF(r1) - ld r12,STK_PARAM(R12)(r1) - li r0,MSR_IR|MSR_DR|MSR_LE - andc r12,r12,r0 LOAD_REG_ADDR(r11, opal_return) mtlr r11 LOAD_REG_ADDR(r11, opal) ld r2,0(r11) ld r11,8(r11) mtspr SPRN_HSRR0,r11 - mtspr SPRN_HSRR1,r12 + /* set token to r0 */ ld r0,STK_PARAM(R11)(r1) + + /* + * We need to keep the MSR value in a register that is preserved by + * OPAL, so that we don't need to access the stack before we restore + * the MSR, as the stack may be vmalloced and thus require MMU. + * + * Move the PACA from R13 into the stack red zone, and put MSR in R13. + */ + std r13,-8(r1) + ld r13,STK_PARAM(R12)(r1) + + /* Switch off MMU, LE */ + li r11,MSR_IR|MSR_DR|MSR_LE + andc r11,r13,r11 + + mtspr SPRN_HSRR1,r11 hrfid opal_return: /* * Restore MSR on OPAL return. The MSR is set to big-endian. */ #ifdef __BIG_ENDIAN__ - ld r11,STK_PARAM(R12)(r1) - mtmsrd r11 + mtmsrd r13 #else /* Endian can only be switched with rfi, must byte reverse MSR load */ - .short 0x4039 /* li r10,STK_PARAM(R12) */ - .byte (STK_PARAM(R12) >> 8) & 0xff - .byte STK_PARAM(R12) & 0xff - - .long 0x280c6a7d /* ldbrx r11,r10,r1 */ - .long 0x05009f42 /* bcl 20,31,$+4 */ - .long 0xa602487d /* mflr r10 */ - .long 0x14004a39 /* addi r10,r10,20 */ - .long 0xa64b5a7d /* mthsrr0 r10 */ - .long 0xa64b7b7d /* mthsrr1 r11 */ - .long 0x2402004c /* hrfid */ + .long 0x05009f42 /* bcl 20,31,$+4 (LR <- next insn addr) */ + .long 0xa602487d /* mflr r10 */ + .long 0x14004a39 /* addi r10,r10,20 (r10 <- addr after #endif) */ + .long 0xa64b5a7d /* mthsrr0 r10 (new NIP) */ + .long 0xa64bbb7d /* mthsrr1 r13 (new MSR) */ + .long 0x2402004c /* hrfid */ #endif + /* Restore PACA */ + ld r13,-8(r1) LOAD_PACA_TOC() ld r0,PPC_LR_STKOFF(r1) mtlr r0
When we enter and return from an OPAL call, there's three pieces of state we have to save and restore: the stack pointer, the PACA pointer, and the MSR. However, there's only two registers that OPAL is guaranteed to preserve for us (r1 for the stack pointer and r13 for the PACA), so the MSR gets saved on the stack. This becomes problematic when we enable VMAP_STACK, as we need to re-enable translation in order to access the virtually mapped stack... and to re-enable translation, we need to restore the MSR. Keep the MSR in r13, and instead store the PACA pointer on the stack - we can restore the MSR first, then restore the PACA into r13. Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com> --- .../powerpc/platforms/powernv/opal-wrappers.S | 43 +++++++++++-------- 1 file changed, 26 insertions(+), 17 deletions(-)