Messages in this thread | | | Date | Sat, 14 Dec 2019 07:29:28 +0800 | From | Baoquan He <> | Subject | Re: [PATCH v5 4/4] x86/mm/KASLR: Adjust the padding size for the direct mapping. |
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On 12/13/19 at 05:38pm, Borislav Petkov wrote: > On Fri, Dec 13, 2019 at 10:54:48PM +0800, Baoquan He wrote: > > On 12/13/19 at 03:15pm, Borislav Petkov wrote: > > > On Fri, Dec 13, 2019 at 09:28:50PM +0800, Baoquan He wrote: > > > > In Documentation/x86/x86_64/mm.rst, the physical memory regions mapping > > > > with page_offset is called as the direct mapping of physical memory. > > > > > > The fact that it happens to compute the *first* region's size, which > > > *happens* to be the direct mapping of all physical memory is immaterial > > > here. > > > > > > It is actually causing more confusion in an already complex piece of > > > code. You can call this function just as well > > > > > > calc_region_size() > > > > > > which won't confuse readers. Because all you care about here is the > > > region's size - not which region it is. > > > > Won't calc_region_size be too generic? We also have vmalloc and vmemmap, > > and here we are specifically calculating the direct mapping of physical > > memory. > > It sounds like you didn't read what I wrote above so read it again pls.
Got it, I believe people won't be confused with calc_region_size(). It's fine to me.
> > > If not knowing the max address to cover all the possible hotplugged > > memory, later memory hotplug will fail. > > You don't have to state the obvious - I can see that in the code. > > So let me ask you differently: can the parsing of the SRAT table happen > shortly before kernel_randomize_memory() *without* adding all that gunk > to the compressed stage, and without adding the boot_params member and > done only for memory hot_add machines?
OK, you mean parsing SRAT again before kernel_randomize_memory(). I think this is what Masa made this patchset to avoid. Then we will have three times SRAT parsing. Passing the max addr from boot to kernel_randomize_memory() was raised when review Chao Fan's patchset, I vaguely remember. Chao didn't take the SRAT parsing way in boot code firstly, later someone suggested to parse, and said the issue in kernel_randomize_memory() can be fixed with the parsed value.
Surely, parsing SRAT here is also good. Maybe Masa can make a draft patch, let people see what it looks like.
Thanks Baoquan
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