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 <a...@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
