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Re: [Qemu-devel] [PATCH] linux-user: do setrlimit selectively

From: Max Filippov
Subject: Re: [Qemu-devel] [PATCH] linux-user: do setrlimit selectively
Date: Tue, 4 Sep 2018 15:26:39 -0700

On Tue, Sep 4, 2018 at 3:10 PM, Peter Maydell <address@hidden> wrote:
> On 4 September 2018 at 23:02, Max Filippov <address@hidden> wrote:
>> On Tue, Sep 4, 2018 at 2:13 PM, Peter Maydell <address@hidden> wrote:
>>> I think the issue here is not related to 32-on-64 but to the fact
>>> that we just pass through the memory rlimits. What we should ideally
>>> be doing is tracking the actual guest memory allocations sufficiently
>>> that we can then apply the rlimits at the QEMU level, so that guest
>>> allocations that breach limits can be failed, without ever causing
>>> QEMU's own alloactions to fail.
>> In a sense we do it by limiting 32-bit guest to 32 or less bits of the 
>> address
>> space, that's why it should be rather safe to just ignore setrlimit calls in
>> 32-on-64 case.
> I'm not sure why you think that we should treat 32-on-64 differently.

I'm not sure, it's just that I have a case that I'd like to fix, and
it's 32-on 64.

> You could make a case for always ignoring setrlimit calls: if we
> ever hit the limit it's as likely to be by failing a QEMU internal
> allocation as a guest one, so not to imposing the limit at all
> would avoid QEMU failing then. But that would apply in both the
> 32-on-64 and also 32-on-32 and 64-on-64 cases too.

That's what I did initially, but it feels somewhat unsafe in 64-on-64 case.
My expectation is that limits set by 64-bit guest should be somewhat
suitable for the 64-bit host, is it wrong?

-- Max

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