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accel/tcg: Fix the comment for CPUTLBEntryFull

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When memory region is ram, the lower TARGET_PAGE_BITS is not the
physical section number. Instead, its value is always 0.

Add comment and assert to make it clear.

Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Message-Id: <20230901060118.379-1-zhiwei_liu@linux.alibaba.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
LIU Zhiwei 2023-09-01 14:01:18 +08:00 committed by Richard Henderson
parent 0e5903436d
commit dff1ab68d8
2 changed files with 13 additions and 10 deletions
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11
accel/tcg/cputlb.c
View File

@ -1193,6 +1193,7 @@ void tlb_set_page_full(CPUState *cpu, int mmu_idx,
write_flags = read_flags;
if (is_ram) {
iotlb = memory_region_get_ram_addr(section->mr) + xlat;
assert(!(iotlb & ~TARGET_PAGE_MASK));
/*
* Computing is_clean is expensive; avoid all that unless
* the page is actually writable.
@ -1255,10 +1256,12 @@ void tlb_set_page_full(CPUState *cpu, int mmu_idx,
/* 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 (RAM)
* + the offset within section->mr of the page base (I/O, ROMD)
* When memory region is ram, iotlb contains a TARGET_PAGE_BITS
* aligned ram_addr_t of the page base of the target RAM.
* Otherwise, iotlb contains
* - a physical section number in the lower TARGET_PAGE_BITS
* - the offset within section->mr of the page base (I/O, ROMD) with the
* TARGET_PAGE_BITS masked off.
* We subtract addr_page (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

12
include/exec/cpu-defs.h
View File

@ -100,12 +100,12 @@
typedef struct CPUTLBEntryFull {
/*
* @xlat_section contains:
* - in the lower TARGET_PAGE_BITS, a physical section number
* - with the lower TARGET_PAGE_BITS masked off, an offset which
* must be added to the virtual address to obtain:
* + the ram_addr_t of the target RAM (if the physical section
* number is PHYS_SECTION_NOTDIRTY or PHYS_SECTION_ROM)
* + the offset within the target MemoryRegion (otherwise)
* - For ram, an offset which must be added to the virtual address
* to obtain the ram_addr_t of the target RAM
* - For other memory regions,
* + in the lower TARGET_PAGE_BITS, the physical section number
* + with the TARGET_PAGE_BITS masked off, the offset within
* the target MemoryRegion
*/
hwaddr xlat_section;