On Thu, Feb 04, 2021 at 07:45:19PM +0100, Daniel Vetter wrote: > PTE insertion is fundamentally racy, and this check doesn't do > anything useful. Quoting Sean: > > "Yeah, it can be whacked. The original, never-upstreamed code asserted that > the > resolved PFN matched the PFN being installed by the fault handler as a sanity > check on the SGX driver's EPC management. The WARN assertion got dropped for > whatever reason, leaving that useless chunk."
Love the "whatever reason" part :-) Shame, I was *going to* rip this off maybe around iteration v40. I have no idea why I did not. Even backtraced years old email threads from lore. Probably just forgot to remove it. So, yeah, I fully agree removing it. Reviewed-by: Jarkko Sakkinen <[email protected]> > Jason stumbled over this as a new user of follow_pfn, and I'm trying > to get rid of unsafe callers of that function so it can be locked down > further. > > This is independent prep work for the referenced patch series. Apologies, consider it my bad... /Jarkko > > References: > https://lore.kernel.org/dri-devel/[email protected]/ > Reported-by: Jason Gunthorpe <[email protected]> > Cc: Jason Gunthorpe <[email protected]> > Cc: Sean Christopherson <[email protected]> > Fixes: 947c6e11fa43 ("x86/sgx: Add ptrace() support for the SGX driver") > Cc: Jarkko Sakkinen <[email protected]> > Cc: Borislav Petkov <[email protected]> > Cc: [email protected] > Signed-off-by: Daniel Vetter <[email protected]> > --- > arch/x86/kernel/cpu/sgx/encl.c | 8 -------- > 1 file changed, 8 deletions(-) > > diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c > index ee50a5010277..20a2dd5ba2b4 100644 > --- a/arch/x86/kernel/cpu/sgx/encl.c > +++ b/arch/x86/kernel/cpu/sgx/encl.c > @@ -141,7 +141,6 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf) > struct sgx_encl_page *entry; > unsigned long phys_addr; > struct sgx_encl *encl; > - unsigned long pfn; > vm_fault_t ret; > > encl = vma->vm_private_data; > @@ -168,13 +167,6 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf) > > phys_addr = sgx_get_epc_phys_addr(entry->epc_page); > > - /* Check if another thread got here first to insert the PTE. */ > - if (!follow_pfn(vma, addr, &pfn)) { > - mutex_unlock(&encl->lock); > - > - return VM_FAULT_NOPAGE; > - } > - > ret = vmf_insert_pfn(vma, addr, PFN_DOWN(phys_addr)); > if (ret != VM_FAULT_NOPAGE) { > mutex_unlock(&encl->lock); > -- > 2.30.0 > >
