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Re: [Qemu-devel] [PATCH] TCG: Fix TB invalidation after breakpoint inser

From: Max Filippov
Subject: Re: [Qemu-devel] [PATCH] TCG: Fix TB invalidation after breakpoint insertion/deletion
Date: Thu, 24 May 2012 18:11:14 +0400

On Thu, May 24, 2012 at 5:26 PM, Jan Kiszka <address@hidden> wrote:
> On 2012-05-24 09:42, Max Filippov wrote:
>> On Thu, May 24, 2012 at 4:16 PM, Jan Kiszka <address@hidden> wrote:
>>> On 2012-05-24 09:08, Max Filippov wrote:
>>>> On Thu, May 24, 2012 at 3:25 PM, Jan Kiszka <address@hidden> wrote:
>>>>> On 2012-05-24 07:51, Max Filippov wrote:
>>>>>> On Thu, May 24, 2012 at 6:34 AM, Jan Kiszka <address@hidden> wrote:
>>>>>>> From: Jan Kiszka <address@hidden>
>>>>>>> tb_invalidate_phys_addr has to called with the exact physical address of
>>>>>>> the breakpoint we add/remove, not just the page's base address.
>>>>>>> Otherwise we easily fail to flush the right TB.
>>>>>>> Regression of 1e7855a558.
>>>>>> Sorry, I fail to see how 1e7855a558 could introduce a regression, it
>>>>>> just rearranged the code.
>>>>>> Even more, AFAIK cpu_get_phys_page_debug returns complete physical
>>>>>> address, not just
>>>>>> physical page. Probably it has a misleading name.
>>>>> Unfortunately, cpu_get_phys_page_debug does NOT deliver the sub-page
>>>>> offset, only the page base address.
>>>> Ok, i386 has probably the most explicit implementation,
>>>> let's look at the target-i386/helper.c:876
>>>>     page_offset = (addr & TARGET_PAGE_MASK) & (page_size - 1);
>>>>     paddr = (pte & TARGET_PAGE_MASK) + page_offset;
>>>>     return paddr;
>>>> that's clearly physical page plus in-page offset.
>>>> I can provide other samples (:
>>> "page_offset" is misleading: addr & TARGET_PAGE_MASK kills all the
>>> offset bits. It will only contain the relevant bits between page_size
>>> Check also ppc's cpu_get_phys_page_debug, it's clearer in this regard.
>> Ok, for i386, ppc, microblaze (and maybe others) you're right.
>> What about ARM, CRIS, MIPS, SH4, xtensa (and maybe others)?
>> Looks like this is a long-standing discrepancy and consequently
>> a long-standing bug in the breakpoint_invalidate.
> Not in breakpoint_invalidate as the missing offset was compensated
> before your commit (well, starting with c2f07f81a2 in fact).

I'd say that compensation that you mention

    ram_addr = (memory_region_get_ram_addr(section.mr)
                + section.offset_within_region) & TARGET_PAGE_MASK;
this >>>>    ram_addr |= (pc & ~TARGET_PAGE_MASK);
    tb_invalidate_phys_page_range(ram_addr, ram_addr + 1, 0);

was removed by f3705d53296d, not by 1e7855a558

> But it looks like cpu_get_phys_page_debug was broken for quite a while.
> Let's fix those archs to return more than page-aligned addresses.

You mean make them all return full physical address?
I'd propose to rename the function then as well.

-- Max

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