| Message ID | 1357219038-841-1-git-send-email-agraf@suse.de |
|---|---|
| State | New |
| Headers | show |
On 3 January 2013 13:17, Alexander Graf <agraf@suse.de> wrote: > MIPS only supports 31 bits of virtual address space for user space, so let's > make sure we stay within that limit with our preallocated memory block. > > This fixes the MIPS user space targets when executed without command line > option. This looks weird -- why should the guest care that we've reserved a 4GB block which it only uses half of? Or is the problem that host mmap() ends up handing out addresses from anywhere in the 4GB reserved area? -- PMM
On 03.01.2013, at 18:19, Peter Maydell wrote: > On 3 January 2013 13:17, Alexander Graf <agraf@suse.de> wrote: >> MIPS only supports 31 bits of virtual address space for user space, so let's >> make sure we stay within that limit with our preallocated memory block. >> >> This fixes the MIPS user space targets when executed without command line >> option. > > This looks weird -- why should the guest care that we've reserved a > 4GB block which it only uses half of? Or is the problem that host > mmap() ends up handing out addresses from anywhere in the 4GB > reserved area? Even worse, it starts from the top IIRC. MIPS uses the upper virtual address bit for kernel/user space indication. I'm not sure where exactly this logic falls apart in our case, but user space virtual addresses above 2GB are simple illegal in that world, so I wouldn't expect QEMU or a guest process to cope with them. Alex
On 01/03/2013 09:24 AM, Alexander Graf wrote: > On 03.01.2013, at 18:19, Peter Maydell wrote: > >> On 3 January 2013 13:17, Alexander Graf<agraf@suse.de> wrote: >>> MIPS only supports 31 bits of virtual address space for user space, so let's >>> make sure we stay within that limit with our preallocated memory block. >>> >>> This fixes the MIPS user space targets when executed without command line >>> option. >> This looks weird -- why should the guest care that we've reserved a >> 4GB block which it only uses half of? Or is the problem that host >> mmap() ends up handing out addresses from anywhere in the 4GB >> reserved area? > Even worse, it starts from the top IIRC. > > MIPS uses the upper virtual address bit for kernel/user space indication. I'm not sure where exactly this logic falls apart in our case, but user space virtual addresses above 2GB are simple illegal in that world, so I wouldn't expect QEMU or a guest process to cope with them. > > > Alex > > While making this change please keep in mind that newer MIPS32 processors allow more than 31 bits of user address space (up to 3.5 GiB) if they have Enhanced Virtual Address support. For example see the Software User's Manual for the interAptiv processors: At the bottom of the page http://www.mips.com/products/processor-cores/aptiv/interaptiv/ is the link interAptiv^(TM) Multiprocessing System Software User's Manual <http://www.mips.com/secure-download/index.dot?product_name=/auth/MD00904-2B-interAptiv-SUM-01.04.pdf> Go to section 1.2.7.5 Enhanced Virtual Address Eric
On 01/03/2013 10:39 AM, Eric Johnson wrote: > While making this change please keep in mind that newer MIPS32 > processors allow more than 31 bits of user address space (up to 3.5 > GiB) if they have Enhanced Virtual Address support. Interesting. Well, would you be able to help figure out exactly what's going on in: http://lists.gnu.org/archive/html/qemu-devel/2012-12/msg03233.html and the thread leading up to it? Now, I don't *know* that this is an emulation failure -- the linux-user-test binary certainly isn't aware of enhanced virtual addresses. So it's possible that (older?) binaries can't cope with more than 2GB. Alternately, it really is a translation problem somewhere... r~
On 01/03/2013 10:50 AM, Richard Henderson wrote: > On 01/03/2013 10:39 AM, Eric Johnson wrote: >> While making this change please keep in mind that newer MIPS32 >> processors allow more than 31 bits of user address space (up to 3.5 >> GiB) if they have Enhanced Virtual Address support. > Interesting. > > Well, would you be able to help figure out exactly what's going on in: > > http://lists.gnu.org/archive/html/qemu-devel/2012-12/msg03233.html > > and the thread leading up to it? > > Now, I don't *know* that this is an emulation failure -- the linux-user-test > binary certainly isn't aware of enhanced virtual addresses. So it's > possible that (older?) binaries can't cope with more than 2GB. > > Alternately, it really is a translation problem somewhere... > > > r~ That is correct. The current test and MIPS32 processors supported by QEMU do not support more than 2 GiB of user space. I didn't mean to imply otherwise. Looking at the MIPS32 processor linux-user on a 64-bit host issue is already on my long list of tasks. Sorry I have not been able to look at it yet. On second thought ignore my EVA comment for now. We'll worry about that when implementing EVA. Eric
On Thu, Jan 03, 2013 at 02:17:18PM +0100, Alexander Graf wrote: > MIPS only supports 31 bits of virtual address space for user space, so let's > make sure we stay within that limit with our preallocated memory block. > > This fixes the MIPS user space targets when executed without command line > option. > > Signed-off-by: Alexander Graf <agraf@suse.de> > --- > linux-user/main.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/linux-user/main.c b/linux-user/main.c > index c4d10ac..a2bc09d 100644 > --- a/linux-user/main.c > +++ b/linux-user/main.c > @@ -57,7 +57,12 @@ int have_guest_base; > * This way we will never overlap with our own libraries or binaries or stack > * or anything else that QEMU maps. > */ > +# ifdef TARGET_MIPS > +/* MIPS only supports 31 bits of virtual address space for user space */ > +unsigned long reserved_va = 0x77000000; > +# else > unsigned long reserved_va = 0xf7000000; > +# endif > #else > unsigned long reserved_va; > #endif Thanks, applied.
diff --git a/linux-user/main.c b/linux-user/main.c index c4d10ac..a2bc09d 100644 --- a/linux-user/main.c +++ b/linux-user/main.c @@ -57,7 +57,12 @@ int have_guest_base; * This way we will never overlap with our own libraries or binaries or stack * or anything else that QEMU maps. */ +# ifdef TARGET_MIPS +/* MIPS only supports 31 bits of virtual address space for user space */ +unsigned long reserved_va = 0x77000000; +# else unsigned long reserved_va = 0xf7000000; +# endif #else unsigned long reserved_va; #endif
MIPS only supports 31 bits of virtual address space for user space, so let's make sure we stay within that limit with our preallocated memory block. This fixes the MIPS user space targets when executed without command line option. Signed-off-by: Alexander Graf <agraf@suse.de> --- linux-user/main.c | 5 +++++ 1 file changed, 5 insertions(+)