Messages in this thread | | | Subject | Re: [PATCH v2 1/1] arm64: mm: correct the inside linear map boundaries during hotplug check | From | Anshuman Khandual <> | Date | Tue, 16 Feb 2021 08:42:26 +0530 |
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On 2/16/21 1:21 AM, Pavel Tatashin wrote: > On Mon, Feb 15, 2021 at 2:34 PM Ard Biesheuvel <ardb@kernel.org> wrote: >> >> On Mon, 15 Feb 2021 at 20:30, Pavel Tatashin <pasha.tatashin@soleen.com> wrote: >>> >>>> Can't we simply use signed arithmetic here? This expression works fine >>>> if the quantities are all interpreted as s64 instead of u64 >>> >>> I was thinking about that, but I do not like the idea of using sign >>> arithmetics for physical addresses. Also, I am worried that someone in >>> the future will unknowingly change it to unsigns or to phys_addr_t. It >>> is safer to have start explicitly set to 0 in case of wrap. >> >> memstart_addr is already a s64 for this exact reason. > > memstart_addr is basically an offset and it must be negative. For > example, this would not work if it was not signed: > #define vmemmap ((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT)) > > However, on powerpc it is phys_addr_t type. > >> >> Btw, the KASLR check is incorrect: memstart_addr could also be >> negative when running the 52-bit VA kernel on hardware that is only >> 48-bit VA capable. > > Good point! > > if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52)) > memstart_addr -= _PAGE_OFFSET(48) - _PAGE_OFFSET(52); > > So, I will remove IS_ENABLED(CONFIG_RANDOMIZE_BASE) again. > > I am OK to change start_linear_pa, end_linear_pa to signed, but IMO > what I have now is actually safer to make sure that does not break > again in the future. An explicit check for the flip over and providing two different start addresses points would be required in order to use the new framework.
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