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Re: [Qemu-devel] guest physical address equal host virtual address ?


From: Blue Swirl
Subject: Re: [Qemu-devel] guest physical address equal host virtual address ?
Date: Wed, 27 Oct 2010 20:22:35 +0000

On Wed, Oct 27, 2010 at 6:14 AM,  <address@hidden> wrote:
>
>>As I remember it, it's on the lines of:
>
>>tlb_entry = env->tlb_table[mem_index][hash(guest_virtual_address)];
>>if (tlb_entry.<access_type> == guest_virtual_address) {
>>   host_virtual_address = tlb_entry.addend
>>} else {
>>  call the slow path through __ld routines
>>}
>
> No,  At qemu-0.10.0
>         host_virtual_addres = guest virtual address + tlb_entry.addend
> not as :
>          host_virtual_address = tlb_entry.addend
>
> Can you explain more?

This is the TLB calculation when taking out checks, for the RAM address case:
    index = (addr >> TARGET_PAGE_BITS) & (CPU_TLB_SIZE - 1);
    tlb_addr = env->tlb_table[mmu_idx][index].ADDR_READ;
            addend = env->tlb_table[mmu_idx][index].addend;
            res = glue(glue(ld, USUFFIX), _raw)((uint8_t *)(long)(addr+addend));

TLB addend is calculated in exec.c, tlb_set_page():
    addend = (unsigned long)qemu_get_ram_ptr(pd & TARGET_PAGE_MASK);
    te->addend = addend - vaddr;

So taking into account both, the virtual address is subtracted,
leaving only host pointer to RAM area.



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