Some of the interrupt vectors on 64-bit POWER server processors are only 32 bytes long (8 instructions), which is not enough for the full first-level interrupt handler. For these we need to branch to an out- of-line (OOL) handler. But when we are running a relocatable kernel, interrupt vectors till __end_interrupts marker are copied down to real address 0x100. So, branching to labels (read OOL handlers) outside this section should be handled differently (see LOAD_HANDLER()), considering relocatable kernel, which would need atleast 4 instructions.
However, branching from interrupt vector means that we corrupt the CFAR (come-from address register) on POWER7 and later processors as mentioned in commit 1707dd16. So, EXCEPTION_PROLOG_0 (6 instructions) that contains the part up to the point where the CFAR is saved in the PACA should be part of the short interrupt vectors before we branch out to OOL handlers. But as mentioned already, there are interrupt vectors on 64-bit POWER server processors that are only 32 bytes long (like vectors 0x4f00, 0x4f20, etc.), which cannot accomodate the above two cases at the same time owing to space constraint. Currently, in these interrupt vectors, we simply branch out to OOL handlers, without using LOAD_HANDLER(), which leaves us vulnerable when running a relocatable kernel (eg. kdump case). While this has been the case for sometime now and kdump is used widely, we were fortunate not to see any problems so far, for three reasons: 1. In almost all cases, production kernel (relocatable) is used for kdump as well, which would mean that crashed kernel's OOL handler would be at the same place where we endup branching to, from short interrupt vector of kdump kernel. 2. Also, OOL handler was unlikely the reason for crash in almost all the kdump scenarios, which meant we had a sane OOL handler from crashed kernel that we branched to. 3. On most 64-bit POWER server processors, page size is large enough that marking interrupt vector code as executable (see commit 429d2e83) leads to marking OOL handler code from crashed kernel, that sits right below interrupt vector code from kdump kernel, as executable as well. Let us fix this undependable code path firstly, by moving down __end_handlers marker down past OOL handlers. Secondly, copying interrupt vectors down till __end_handlers marker instead of __end_interrupts, when running a relocatable kernel, to make sure we endup in relocated (kdump) kernel's OOL handler instead of crashed kernel's. Thirdly, by marking all the interrupt vector code that is copied down to real address 0x100 as executable, considering the relocation on exception feature that allows exceptions to be raised in virtual mode (IR=DR=1). This fix has been tested successfully in kdump scenario, on a lpar with 4K page size by using different default/production kernel and kdump kernel. Signed-off-by: Hari Bathini <hbath...@linux.vnet.ibm.com> Signed-off-by: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com> --- arch/powerpc/include/asm/sections.h | 3 ++- arch/powerpc/kernel/exceptions-64s.S | 8 ++++---- arch/powerpc/kernel/head_64.S | 2 +- 3 files changed, 7 insertions(+), 6 deletions(-) diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h index abf5866..b4139a5 100644 --- a/arch/powerpc/include/asm/sections.h +++ b/arch/powerpc/include/asm/sections.h @@ -10,6 +10,7 @@ extern char __start_interrupts[]; extern char __end_interrupts[]; +extern char __end_handlers[]; extern char __prom_init_toc_start[]; extern char __prom_init_toc_end[]; @@ -39,7 +40,7 @@ static inline int overlaps_interrupt_vector_text(unsigned long start, { unsigned long real_start, real_end; real_start = __start_interrupts - _stext; - real_end = __end_interrupts - _stext; + real_end = __end_handlers - _stext; return start < (unsigned long)__va(real_end) && (unsigned long)__va(real_start) < end; diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index 7716ceb..98e2ce5 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -1230,10 +1230,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_VSX) STD_EXCEPTION_COMMON(0xf60, facility_unavailable, facility_unavailable_exception) STD_EXCEPTION_COMMON(0xf80, hv_facility_unavailable, facility_unavailable_exception) - .align 7 - .globl __end_handlers -__end_handlers: - /* Equivalents to the above handlers for relocation-on interrupt vectors */ STD_RELON_EXCEPTION_HV_OOL(0xe40, emulation_assist) MASKABLE_RELON_EXCEPTION_HV_OOL(0xe80, h_doorbell) @@ -1244,6 +1240,10 @@ __end_handlers: STD_RELON_EXCEPTION_PSERIES_OOL(0xf60, facility_unavailable) STD_RELON_EXCEPTION_HV_OOL(0xf80, hv_facility_unavailable) + .align 7 + .globl __end_handlers +__end_handlers: + #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_PPC_POWERNV) /* * Data area reserved for FWNMI option. diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S index 4286775..829c74c 100644 --- a/arch/powerpc/kernel/head_64.S +++ b/arch/powerpc/kernel/head_64.S @@ -611,7 +611,7 @@ __after_prom_start: sub r5,r5,r11 #else /* just copy interrupts */ - LOAD_REG_IMMEDIATE(r5, __end_interrupts - _stext) + LOAD_REG_IMMEDIATE(r5, __end_handlers - _stext) #endif b 5f 3: _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev