On Wed, May 26, 2021, at 2:14 PM, Babu Moger wrote:
On 5/25/21 7:36 PM, Andy Lutomirski wrote:
On 5/25/21 2:37 PM, Babu Moger wrote:
Investigation so far.
- The test fails on AMD(Milan) systems. Test appears to pass on Intel
systems. Tested on old Intel system available here.
Ten cents says that you have discovered that AMD returns a synthesized value for XINUSE[PKRU] and that write_pkru() is buggy.
Any volunteers to fix the if (!pk) case in write_pkru() and see if the problem goes away? (Or at least to print something for the if (!pk) case and seee if it gets printed?)
I inserted this patch to test this path.
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index b1099f2d9800..a0bca917f864 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -151,6 +160,8 @@ static inline void write_pkru(u32 pkru) fpregs_lock(); if (pk) pk->pkru = pkru;
elseprintk_once("%s read_pkru 0x%x\n",__FUNCTION__, read_pkru()); __write_pkru(pkru); fpregs_unlock();}
Yes. The pk value is sometimes NULL and the value in the pkru register is 0 at that time. Here is the dmesg output.
[ 1.700889] write_pkru read_pkru 0x0
Sweet, maybe I get my hypothetical dime back! Both bugs are real.
Dave and I (mostly Dave — I’m supplying the snark) are working on an omnibus patch to fix this whole mess.
Thanks, Andy