From 80313b3078fcd2ca51970880d90757f05879a193 Mon Sep 17 00:00:00 2001 From: Stefan Lippers-Hollmann Date: Mon, 30 Mar 2015 22:44:27 +0200 Subject: x86/reboot: Add ASRock Q1900DC-ITX mainboard reboot quirk The ASRock Q1900DC-ITX mainboard (Baytrail-D) hangs randomly in both BIOS and UEFI mode while rebooting unless reboot=pci is used. Add a quirk to reboot via the pci method. The problem is very intermittent and hard to debug, it might succeed rebooting just fine 40 times in a row - but fails half a dozen times the next day. It seems to be slightly less common in BIOS CSM mode than native UEFI (with the CSM disabled), but it does happen in either mode. Since I've started testing this patch in late january, rebooting has been 100% reliable. Most of the time it already hangs during POST, but occasionally it might even make it through the bootloader and the kernel might even start booting, but then hangs before the mode switch. The same symptoms occur with grub-efi, gummiboot and grub-pc, just as well as (at least) kernel 3.16-3.19 and 4.0-rc6 (I haven't tried older kernels than 3.16). Upgrading to the most current mainboard firmware of the ASRock Q1900DC-ITX, version 1.20, does not improve the situation. ( Searching the web seems to suggest that other Bay Trail-D mainboards might be affected as well. ) -- Signed-off-by: Stefan Lippers-Hollmann Cc: Cc: Matt Fleming Link: http://lkml.kernel.org/r/20150330224427.0fb58e42@mir Signed-off-by: Ingo Molnar --- arch/x86/kernel/reboot.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'arch') diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c index bae6c609888e..86db4bcd7ce5 100644 --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -183,6 +183,16 @@ static struct dmi_system_id __initdata reboot_dmi_table[] = { }, }, + /* ASRock */ + { /* Handle problems with rebooting on ASRock Q1900DC-ITX */ + .callback = set_pci_reboot, + .ident = "ASRock Q1900DC-ITX", + .matches = { + DMI_MATCH(DMI_BOARD_VENDOR, "ASRock"), + DMI_MATCH(DMI_BOARD_NAME, "Q1900DC-ITX"), + }, + }, + /* ASUS */ { /* Handle problems with rebooting on ASUS P4S800 */ .callback = set_bios_reboot, -- cgit v1.2.3 From 7ea24169097d3d3a3eab2dcc5773bc43fd5593e7 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 1 Apr 2015 14:26:34 -0700 Subject: x86/asm/entry/64: Disable opportunistic SYSRET if regs->flags has TF set When I wrote the opportunistic SYSRET code, I missed an important difference between SYSRET and IRET. Both instructions are capable of setting EFLAGS.TF, but they behave differently when doing so: - IRET will not issue a #DB trap after execution when it sets TF. This is critical -- otherwise you'd never be able to make forward progress when returning to userspace. - SYSRET, on the other hand, will trap with #DB immediately after returning to CPL3, and the next instruction will never execute. This breaks anything that opportunistically SYSRETs to a user context with TF set. For example, running this code with TF set and a SIGTRAP handler loaded never gets past 'post_nop': extern unsigned char post_nop[]; asm volatile ("pushfq\n\t" "popq %%r11\n\t" "nop\n\t" "post_nop:" : : "c" (post_nop) : "r11"); In my defense, I can't find this documented in the AMD or Intel manual. Fix it by using IRET to restore TF. Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Thomas Gleixner Fixes: 2a23c6b8a9c4 ("x86_64, entry: Use sysret to return to userspace when possible") Link: http://lkml.kernel.org/r/9472f1ca4c19a38ecda45bba9c91b7168135fcfa.1427923514.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/kernel/entry_64.S | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 2babb393915e..f0095a76c182 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -799,7 +799,21 @@ retint_swapgs: /* return to user-space */ cmpq %r11,(EFLAGS-ARGOFFSET)(%rsp) /* R11 == RFLAGS */ jne opportunistic_sysret_failed - testq $X86_EFLAGS_RF,%r11 /* sysret can't restore RF */ + /* + * SYSRET can't restore RF. SYSRET can restore TF, but unlike IRET, + * restoring TF results in a trap from userspace immediately after + * SYSRET. This would cause an infinite loop whenever #DB happens + * with register state that satisfies the opportunistic SYSRET + * conditions. For example, single-stepping this user code: + * + * movq $stuck_here,%rcx + * pushfq + * popq %r11 + * stuck_here: + * + * would never get past 'stuck_here'. + */ + testq $(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11 jnz opportunistic_sysret_failed /* nothing to check for RSP */ -- cgit v1.2.3 From f59df35fc28167886a0caf9f15db2f4a1f5932da Mon Sep 17 00:00:00 2001 From: Steffen Liebergeld Date: Thu, 2 Apr 2015 11:01:59 +0200 Subject: kgdb/x86: Fix reporting of 'si' in kgdb on x86_64 This patch fixes an error in kgdb for x86_64 which would report the value of dx when asked to give the value of si. Signed-off-by: Steffen Liebergeld Cc: Jason Wessel Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- arch/x86/kernel/kgdb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c index 7ec1d5f8d283..25ecd56cefa8 100644 --- a/arch/x86/kernel/kgdb.c +++ b/arch/x86/kernel/kgdb.c @@ -72,7 +72,7 @@ struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = { "bx", 8, offsetof(struct pt_regs, bx) }, { "cx", 8, offsetof(struct pt_regs, cx) }, { "dx", 8, offsetof(struct pt_regs, dx) }, - { "si", 8, offsetof(struct pt_regs, dx) }, + { "si", 8, offsetof(struct pt_regs, si) }, { "di", 8, offsetof(struct pt_regs, di) }, { "bp", 8, offsetof(struct pt_regs, bp) }, { "sp", 8, offsetof(struct pt_regs, sp) }, -- cgit v1.2.3