Re: Flushing user entries for kernel mappings in x86
at 8:45 PM, Andy Lutomirski wrote: > On Tue, Aug 28, 2018 at 6:46 PM, Nadav Amit wrote: >> Hello Andy, >> >> Is there a reason for __flush_tlb_one_kernel() to flush the PTE not only in >> the kernel address space, but also in the user one (as part of >> __flush_tlb_one_user)? [ I obviously regard the case when PTI is on ]. > > In most cases, probably not, but it's fairly cheap, I think. And it > makes it so that we're okay if the TLB entry we're flushing is used by > the entry code. Thanks. I assumed that’s the case. I don’t know how cheap they are (especially if INVPCID is not supported) but I guess they are not that frequent.
Re: Flushing user entries for kernel mappings in x86
at 8:45 PM, Andy Lutomirski wrote: > On Tue, Aug 28, 2018 at 6:46 PM, Nadav Amit wrote: >> Hello Andy, >> >> Is there a reason for __flush_tlb_one_kernel() to flush the PTE not only in >> the kernel address space, but also in the user one (as part of >> __flush_tlb_one_user)? [ I obviously regard the case when PTI is on ]. > > In most cases, probably not, but it's fairly cheap, I think. And it > makes it so that we're okay if the TLB entry we're flushing is used by > the entry code. Thanks. I assumed that’s the case. I don’t know how cheap they are (especially if INVPCID is not supported) but I guess they are not that frequent.
Re: Flushing user entries for kernel mappings in x86
On Tue, Aug 28, 2018 at 6:46 PM, Nadav Amit wrote: > Hello Andy, > > Is there a reason for __flush_tlb_one_kernel() to flush the PTE not only in > the kernel address space, but also in the user one (as part of > __flush_tlb_one_user)? [ I obviously regard the case when PTI is on ]. In most cases, probably not, but it's fairly cheap, I think. And it makes it so that we're okay if the TLB entry we're flushing is used by the entry code.
Re: Flushing user entries for kernel mappings in x86
On Tue, Aug 28, 2018 at 6:46 PM, Nadav Amit wrote: > Hello Andy, > > Is there a reason for __flush_tlb_one_kernel() to flush the PTE not only in > the kernel address space, but also in the user one (as part of > __flush_tlb_one_user)? [ I obviously regard the case when PTI is on ]. In most cases, probably not, but it's fairly cheap, I think. And it makes it so that we're okay if the TLB entry we're flushing is used by the entry code.
