Il 09/05/2013 05:41, liu ping fan ha scritto: > On Wed, May 8, 2013 at 12:08 AM, Paolo Bonzini <pbonz...@redhat.com> wrote: >> >> >> ----- Messaggio originale ----- >>> Da: "Peter Maydell" <peter.mayd...@linaro.org> >>> A: "Paolo Bonzini" <pbonz...@redhat.com> >>> Cc: qemu-devel@nongnu.org, a...@ozlabs.ru, "jan kiszka" >>> <jan.kis...@siemens.com>, qemul...@gmail.com, >>> stefa...@redhat.com, da...@gibson.dropbear.id.au >>> Inviato: Martedì, 7 maggio 2013 17:44:59 >>> Oggetto: Re: [Qemu-devel] [PATCH 01/40] memory: assert that PhysPageEntry's >>> ptr does not overflow >>> >>> On 7 May 2013 15:16, Paolo Bonzini <pbonz...@redhat.com> wrote: >>>> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> >>>> --- >>>> exec.c | 2 ++ >>>> 1 files changed, 2 insertions(+), 0 deletions(-) >>>> >>>> diff --git a/exec.c b/exec.c >>>> index 19725db..2e5b89a 100644 >>>> --- a/exec.c >>>> +++ b/exec.c >>>> @@ -719,6 +719,8 @@ static void destroy_all_mappings(AddressSpaceDispatch >>>> *d) >>>> >>>> static uint16_t phys_section_add(MemoryRegionSection *section) >>>> { >>>> + assert(phys_sections_nb < TARGET_PAGE_SIZE); >>>> + >>>> if (phys_sections_nb == phys_sections_nb_alloc) { >>>> phys_sections_nb_alloc = MAX(phys_sections_nb_alloc * 2, 16); >>>> phys_sections = g_renew(MemoryRegionSection, phys_sections, >>> >>> Why is the limit we're asserting not the same as the maximum >>> size that we pass to g_renew() below? >> >> That's a minimum size, isn't it? >> >> I'm asserting that the physical section number doesn't overflow into >> the page, since the TLB entries are stored as a combination of the two. >> > Could you explain more detail? Why < TARGET_PAGE_SIZE, not 2^15?
Because the TLB entry is the "or" of the page address and the phys_section. Look here: hwaddr memory_region_section_get_iotlb(CPUArchState *env, MemoryRegionSection *section, target_ulong vaddr, hwaddr paddr, int prot, target_ulong *address) { hwaddr iotlb; CPUWatchpoint *wp; if (memory_region_is_ram(section->mr)) { /* Normal RAM. */ iotlb = (memory_region_get_ram_addr(section->mr) & TARGET_PAGE_MASK) + memory_region_section_addr(section, paddr); if (!section->readonly) { iotlb |= phys_section_notdirty; } else { iotlb |= phys_section_rom; } } else { iotlb = section - phys_sections; iotlb += memory_region_section_addr(section, paddr); } where the else could be written better as: iotlb = memory_region_section_addr(section, paddr); iotlb |= section - phys_sections; memory_region_section_addr will return a page-aligned value. Paolo