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cpu-defs.h: Document CPUIOTLBEntry 'addr' field

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The 'addr' field in the CPUIOTLBEntry struct has a rather non-obvious
use; add a comment documenting it (reverse-engineered from what
the code that sets it is doing).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180611125633.32755-2-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2018-06-15 14:57:14 +01:00
parent f81804a52b
commit ace4109011
2 changed files with 21 additions and 0 deletions
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12
accel/tcg/cputlb.c
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@ -664,6 +664,18 @@ void tlb_set_page_with_attrs(CPUState *cpu, target_ulong vaddr,
env->iotlb_v[mmu_idx][vidx] = env->iotlb[mmu_idx][index];
/* refill the tlb */
/*
* At this point iotlb contains a physical section number in the lower
* TARGET_PAGE_BITS, and either
* + the ram_addr_t of the page base of the target RAM (if NOTDIRTY or ROM)
* + the offset within section->mr of the page base (otherwise)
* We subtract the vaddr (which is page aligned and thus won't
* disturb the low bits) to give an offset which can be added to the
* (non-page-aligned) vaddr of the eventual memory access to get
* the MemoryRegion offset for the access. Note that the vaddr we
* subtract here is that of the page base, and not the same as the
* vaddr we add back in io_readx()/io_writex()/get_page_addr_code().
*/
env->iotlb[mmu_idx][index].addr = iotlb - vaddr;
env->iotlb[mmu_idx][index].attrs = attrs;