From c9f6e9977e38de15da96b732a8dec0ef56cbf977 Mon Sep 17 00:00:00 2001 From: Roger Pau Monne Date: Mon, 20 Jan 2014 09:20:07 -0500 Subject: [PATCH] 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/enlighten.c | 33 ++++++++++++++++++++++++++++++--- arch/x86/xen/smp.c | 2 +- arch/x86/xen/xen-ops.h | 2 +- 3 files changed, 32 insertions(+), 5 deletions(-) diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index b6d61c353fe5..a4d7b647867f 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -1414,7 +1414,7 @@ static void __init xen_boot_params_init_edd(void) * is PVH which is not going to use xen_load_gdt_boot or other * __init functions. */ -void __ref xen_setup_gdt(int cpu) +static void __ref xen_setup_gdt(int cpu) { if (xen_feature(XENFEAT_auto_translated_physmap)) { #ifdef CONFIG_X86_64 @@ -1462,13 +1462,40 @@ void __ref xen_setup_gdt(int cpu) pv_cpu_ops.load_gdt = xen_load_gdt; } +/* + * A PV guest starts with default flags that are not set for PVH, set them + * here asap. + */ +static void xen_pvh_set_cr_flags(int cpu) +{ + + /* Some of these are setup in 'secondary_startup_64'. The others: + * X86_CR0_TS, X86_CR0_PE, X86_CR0_ET are set by Xen for HVM guests + * (which PVH shared codepaths), while X86_CR0_PG is for PVH. */ + write_cr0(read_cr0() | X86_CR0_MP | X86_CR0_NE | X86_CR0_WP | X86_CR0_AM); +} + +/* + * Note, that it is ref - because the only caller of this after init + * is PVH which is not going to use xen_load_gdt_boot or other + * __init functions. + */ +void __ref xen_pvh_secondary_vcpu_init(int cpu) +{ + xen_setup_gdt(cpu); + xen_pvh_set_cr_flags(cpu); +} + static void __init xen_pvh_early_guest_init(void) { if (!xen_feature(XENFEAT_auto_translated_physmap)) return; - if (xen_feature(XENFEAT_hvm_callback_vector)) - xen_have_vector_callback = 1; + if (!xen_feature(XENFEAT_hvm_callback_vector)) + return; + + xen_have_vector_callback = 1; + xen_pvh_set_cr_flags(0); #ifdef CONFIG_X86_32 BUG(); /* PVH: Implement proper support. */ 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); diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h index 9059c24ed564..1cb6f4c37300 100644 --- a/arch/x86/xen/xen-ops.h +++ b/arch/x86/xen/xen-ops.h @@ -123,5 +123,5 @@ __visible void xen_adjust_exception_frame(void); extern int xen_panic_handler_init(void); -void xen_setup_gdt(int cpu); +void xen_pvh_secondary_vcpu_init(int cpu); #endif /* XEN_OPS_H */ -- 2.39.5