On Tue, Aug 17, 2021 at 11:05:15AM +0200, Thomas Gleixner wrote: > Huacai, > > On Tue, Aug 17 2021 at 15:38, Huacai Chen wrote: > > On Tue, Aug 17, 2021 at 3:07 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > On X86, it returns 0; on MIPS64 without patch, it hangs in kernel; on > > MIPS64 with this patch, it returns -1. > > As expected. > > > Then, I want to know, on "W implies R" archs (such as X86), should it > > return 0? Maybe return -1 is more reasonable? (because the VMA is > > marked as write-only). If this program should return -1, then I don't > > think this is a MIPS-specific problem. > > No. mmap(.., PROT_WRITE...) is simply impossible on x86 and implies > PROT_READ as documented in mmap(2). > > So why should this fail and only fail in the fault case, but succeed > when the PTE is already established? I wouldn't actually mind if it failed on fault -- it's the 'best' we can do on x86. Doing a RmW op on PROT_WRITE is silly and deserves all the wreckage it can get.
