From c9f6e9977e38de15da96b732a8dec0ef56cbf977 Mon Sep 17 00:00:00 2001 From: Roger Pau Monne Date: Mon, 20 Jan 2014 09:20:07 -0500 Subject: xen/pvh: Set X86_CR0_WP and others in CR0 (v2) otherwise we will get for some user-space applications that use 'clone' with CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID end up hitting an assert in glibc manifested by: general protection ip:7f80720d364c sp:7fff98fd8a80 error:0 in libc-2.13.so[7f807209e000+180000] This is due to the nature of said operations which sets and clears the PID. "In the successful one I can see that the page table of the parent process has been updated successfully to use a different physical page, so the write of the tid on that page only affects the child... On the other hand, in the failed case, the write seems to happen before the copy of the original page is done, so both the parent and the child end up with the same value (because the parent copies the page after the write of the child tid has already happened)." (Roger's analysis). The nature of this is due to the Xen's commit of 51e2cac257ec8b4080d89f0855c498cbbd76a5e5 "x86/pvh: set only minimal cr0 and cr4 flags in order to use paging" the CR0_WP was removed so COW features of the Linux kernel were not operating properly. While doing that also update the rest of the CR0 flags to be inline with what a baremetal Linux kernel would set them to. In 'secondary_startup_64' (baremetal Linux) sets: X86_CR0_PE | X86_CR0_MP | X86_CR0_ET | X86_CR0_NE | X86_CR0_WP | X86_CR0_AM | X86_CR0_PG The hypervisor for HVM type guests (which PVH is a bit) sets: X86_CR0_PE | X86_CR0_ET | X86_CR0_TS For PVH it specifically sets: X86_CR0_PG Which means we need to set the rest: X86_CR0_MP | X86_CR0_NE | X86_CR0_WP | X86_CR0_AM to have full parity. Signed-off-by: Roger Pau Monne Signed-off-by: Mukesh Rathor Signed-off-by: Konrad Rzeszutek Wilk [v1: Took out the cr4 writes to be a seperate patch] [v2: 0-DAY kernel found xen_setup_gdt to be missing a static] --- arch/x86/xen/smp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/xen/smp.c') diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c index 5e46190133b2..a18eadd8bb40 100644 --- a/arch/x86/xen/smp.c +++ b/arch/x86/xen/smp.c @@ -105,7 +105,7 @@ static void cpu_bringup_and_idle(int cpu) #ifdef CONFIG_X86_64 if (xen_feature(XENFEAT_auto_translated_physmap) && xen_feature(XENFEAT_supervisor_mode_kernel)) - xen_setup_gdt(cpu); + xen_pvh_secondary_vcpu_init(cpu); #endif cpu_bringup(); cpu_startup_entry(CPUHP_ONLINE); -- cgit v1.2.3