[openib-general] RE: registering read-only memory
Title: RE: registering read-only memory OK thanks. I had another problem in MVAPI. -Original Message- From: Roland Dreier [mailto:[EMAIL PROTECTED]] Sent: Friday, May 27, 2005 7:49 PM To: Eli Cohen Cc: Michael S. Tsirkin; openib-general@openib.org Subject: Re: registering read-only memory Eli> I saw this this on Suse 9.3 and the memory was like: static Eli> const char *my_string = "Hello world"; defined locally in a Eli> function. This produced a VMA with VM_IO set. What kernel version/architecture? I'm having a hard time seeing how it's possible to get a VMA with VM_IO set except by using remap_pfn_range(), and I can't see how ordinary const data from userspace could cause that. - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] Re: registering read-only memory
Eli> I saw this this on Suse 9.3 and the memory was like: static Eli> const char *my_string = "Hello world"; defined locally in a Eli> function. This produced a VMA with VM_IO set. What kernel version/architecture? I'm having a hard time seeing how it's possible to get a VMA with VM_IO set except by using remap_pfn_range(), and I can't see how ordinary const data from userspace could cause that. - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] RE: registering read-only memory
Title: RE: registering read-only memory R> Are you sure? It seems to work for me if I just pass write=0 to R> get_user_pages(). I saw this this on Suse 9.3 and the memory was like: static const char *my_string = "Hello world"; defined locally in a function. This produced a VMA with VM_IO set. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
Re: [openib-general] RE: registering read-only memory
Grant> Sorry - why do you need the physical address of memory? Grant> Did you mean you need the DMA address? We don't really need the physical address. The userspace verbs do get_user_pages() on a userspace virtual address to get a bunch of struct page *s, and then pass those to dma_map_sg() to get DMA addresses. It's all totally kosher... - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
Re: [openib-general] RE: registering read-only memory
On Thu, May 26, 2005 at 10:23:55PM +0300, Eli Cohen wrote: > I'm afraid that won't solve the problem. From some reason the vma of such a > region is flagged with VM_IO and that's why get_user_pages() will fail. We > need to find another way to get the physical address of such memory. Sorry - why do you need the physical address of memory? Did you mean you need the DMA address? grant > One > thing I can think of is implementing something similar to follow_page(). Or > better if the kernel will export follow_page(). > > -Original Message- > From: Roland Dreier [mailto:[EMAIL PROTECTED] > Sent: Thursday, May 26, 2005 10:09 PM > To: Eli Cohen > Cc: Michael S. Tsirkin; openib-general@openib.org > Subject: Re: registering read-only memory > > > OK, I think I understand the problem. The compiler puts a string > defined with "const char *foo" on a read-only page, but in > uverbs_mem.c we always pass write=1 to get_user_pages(). I need to > fix the code so that it only asks for writeable pages if we're > registering with writable permissions. > > - R. > ___ > openib-general mailing list > openib-general@openib.org > http://openib.org/mailman/listinfo/openib-general > > To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] Re: registering read-only memory
Eli> I'm afraid that won't solve the problem. From some reason the Eli> vma of such a region is flagged with VM_IO and that's why Eli> get_user_pages() will fail. Are you sure? It seems to work for me if I just pass write=0 to get_user_pages(). - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] RE: registering read-only memory
Title: RE: registering read-only memory I'm afraid that won't solve the problem. From some reason the vma of such a region is flagged with VM_IO and that's why get_user_pages() will fail. We need to find another way to get the physical address of such memory. One thing I can think of is implementing something similar to follow_page(). Or better if the kernel will export follow_page(). -Original Message- From: Roland Dreier [mailto:[EMAIL PROTECTED]] Sent: Thursday, May 26, 2005 10:09 PM To: Eli Cohen Cc: Michael S. Tsirkin; openib-general@openib.org Subject: Re: registering read-only memory OK, I think I understand the problem. The compiler puts a string defined with "const char *foo" on a read-only page, but in uverbs_mem.c we always pass write=1 to get_user_pages(). I need to fix the code so that it only asks for writeable pages if we're registering with writable permissions. - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
Re: [openib-general] Re: registering read-only memory
I just checked in a fix for this. I'm now able to register read-only memory (as long as the permissions on the registration are read-only). - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] Re: registering read-only memory
OK, I think I understand the problem. The compiler puts a string defined with "const char *foo" on a read-only page, but in uverbs_mem.c we always pass write=1 to get_user_pages(). I need to fix the code so that it only asks for writeable pages if we're registering with writable permissions. - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] RE: registering read-only memory
Title: RE: registering read-only memory Please try: const char *foo="Michael Tsirkin"; as opposed to const char foo[]="Michael Tsirkin"; -Original Message- From: Roland Dreier [mailto:[EMAIL PROTECTED]] Sent: Tuesday, May 24, 2005 10:07 PM To: Michael S. Tsirkin Cc: openib-general@openib.org; Eli Cohen Subject: Re: registering read-only memory > const char foo[]="Michael Tsirkin"; > ibv_reg_mr(ctx->pd, foo, strlen(foo), 0); This seemed to work fine on my system (I got a non-null ibv_mr back with valid-looking L_Key/R_Key). - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] Re: registering read-only memory
> const char foo[]="Michael Tsirkin"; > ibv_reg_mr(ctx->pd, foo, strlen(foo), 0); This seemed to work fine on my system (I got a non-null ibv_mr back with valid-looking L_Key/R_Key). - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] Re: registering read-only memory
Quoting r. Roland Dreier <[EMAIL PROTECTED]>: > Subject: Re: registering read-only memory > > Michael> What about the patch that I posted? > > Adding the "const" makes sense but adding "volatile" doesn't seem good > to me. Could you explain why? Since the library never accesses the data, it has no effect except turning off a warning. Volatile says like "this buffer can change without the application writing there", and thats what we have with hardware writing there, no? > I think it's better for the tiny subset of people who really > need "volatile" to add casts. > > - R. > IMO, you cant always do this. If you have a non-volatile variable and cast it to a volatile pointer, compiler is permitted to detect this and ignore the volatile attribute, making the code that polls data incorrect (I'm not claiming gcc is smart enough to do this, though). -- MST - Michael S. Tsirkin ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] Re: registering read-only memory
Michael> What about the patch that I posted? Adding the "const" makes sense but adding "volatile" doesn't seem good to me. I think it's better for the tiny subset of people who really need "volatile" to add casts. - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] Re: registering read-only memory
Quoting r. Roland Dreier <[EMAIL PROTECTED]>: > Subject: Re: registering read-only memory > > Michael> 2. ibv_reg_mr fails. Why is that? > > Michael> Returns NULL, naturally. > > ... hmm, I'll take a look. > > - R. > What about the patch that I posted? -- MST - Michael S. Tsirkin ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] Re: registering read-only memory
Michael> 2. ibv_reg_mr fails. Why is that? Michael> Returns NULL, naturally. ... hmm, I'll take a look. - R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] Re: registering read-only memory
Quoting r. Roland Dreier <[EMAIL PROTECTED]>: > Subject: Re: registering read-only memory > > Michael> 2. ibv_reg_mr fails. Why is that? > > How does it fail? > > R. > Returns NULL, naturally. -- MST - Michael S. Tsirkin ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
[openib-general] Re: registering read-only memory
Michael> 2. ibv_reg_mr fails. Why is that? How does it fail? R. ___ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
