LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Cornelia Huck <cohuck@redhat.com>
Subject: [PATCH 4.9 34/74] s390: add options to change branch prediction behaviour for the kernel
Date: Fri, 27 Apr 2018 15:58:24 +0200	[thread overview]
Message-ID: <20180427135711.344105030@linuxfoundation.org> (raw)
In-Reply-To: <20180427135709.899303463@linuxfoundation.org>

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Schwidefsky <schwidefsky@de.ibm.com>


[ Upstream commit d768bd892fc8f066cd3aa000eb1867bcf32db0ee ]

Add the PPA instruction to the system entry and exit path to switch
the kernel to a different branch prediction behaviour. The instructions
are added via CPU alternatives and can be disabled with the "nospec"
or the "nobp=0" kernel parameter. If the default behaviour selected
with CONFIG_KERNEL_NOBP is set to "n" then the "nobp=1" parameter can be
used to enable the changed kernel branch prediction.

Acked-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/s390/Kconfig                 |   17 +++++++++++++
 arch/s390/include/asm/processor.h |    1 
 arch/s390/kernel/alternative.c    |   23 ++++++++++++++++++
 arch/s390/kernel/early.c          |    2 +
 arch/s390/kernel/entry.S          |   48 ++++++++++++++++++++++++++++++++++++++
 arch/s390/kernel/ipl.c            |    1 
 arch/s390/kernel/smp.c            |    2 +
 7 files changed, 94 insertions(+)

--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -704,6 +704,23 @@ config SECCOMP
 
 	  If unsure, say Y.
 
+config KERNEL_NOBP
+	def_bool n
+	prompt "Enable modified branch prediction for the kernel by default"
+	help
+	  If this option is selected the kernel will switch to a modified
+	  branch prediction mode if the firmware interface is available.
+	  The modified branch prediction mode improves the behaviour in
+	  regard to speculative execution.
+
+	  With the option enabled the kernel parameter "nobp=0" or "nospec"
+	  can be used to run the kernel in the normal branch prediction mode.
+
+	  With the option disabled the modified branch prediction mode is
+	  enabled with the "nobp=1" kernel parameter.
+
+	  If unsure, say N.
+
 endmenu
 
 menu "Power Management"
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -84,6 +84,7 @@ void cpu_detect_mhz_feature(void);
 extern const struct seq_operations cpuinfo_op;
 extern int sysctl_ieee_emulation_warnings;
 extern void execve_tail(void);
+extern void __bpon(void);
 
 /*
  * User space process size: 2GB for 31 bit, 4TB or 8PT for 64 bit.
--- a/arch/s390/kernel/alternative.c
+++ b/arch/s390/kernel/alternative.c
@@ -14,6 +14,29 @@ static int __init disable_alternative_in
 
 early_param("noaltinstr", disable_alternative_instructions);
 
+static int __init nobp_setup_early(char *str)
+{
+	bool enabled;
+	int rc;
+
+	rc = kstrtobool(str, &enabled);
+	if (rc)
+		return rc;
+	if (enabled && test_facility(82))
+		__set_facility(82, S390_lowcore.alt_stfle_fac_list);
+	else
+		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
+	return 0;
+}
+early_param("nobp", nobp_setup_early);
+
+static int __init nospec_setup_early(char *str)
+{
+	__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
+	return 0;
+}
+early_param("nospec", nospec_setup_early);
+
 struct brcl_insn {
 	u16 opc;
 	s32 disp;
--- a/arch/s390/kernel/early.c
+++ b/arch/s390/kernel/early.c
@@ -302,6 +302,8 @@ static noinline __init void setup_facili
 	memcpy(S390_lowcore.alt_stfle_fac_list,
 	       S390_lowcore.stfle_fac_list,
 	       sizeof(S390_lowcore.alt_stfle_fac_list));
+	if (!IS_ENABLED(CONFIG_KERNEL_NOBP))
+		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
 }
 
 static __init void detect_diag9c(void)
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -163,6 +163,34 @@ _PIF_WORK	= (_PIF_PER_TRAP)
 		tm	off+\addr, \mask
 	.endm
 
+	.macro BPOFF
+	.pushsection .altinstr_replacement, "ax"
+660:	.long	0xb2e8c000
+	.popsection
+661:	.long	0x47000000
+	.pushsection .altinstructions, "a"
+	.long 661b - .
+	.long 660b - .
+	.word 82
+	.byte 4
+	.byte 4
+	.popsection
+	.endm
+
+	.macro BPON
+	.pushsection .altinstr_replacement, "ax"
+662:	.long	0xb2e8d000
+	.popsection
+663:	.long	0x47000000
+	.pushsection .altinstructions, "a"
+	.long 663b - .
+	.long 662b - .
+	.word 82
+	.byte 4
+	.byte 4
+	.popsection
+	.endm
+
 	.section .kprobes.text, "ax"
 .Ldummy:
 	/*
@@ -175,6 +203,11 @@ _PIF_WORK	= (_PIF_PER_TRAP)
 	 */
 	nop	0
 
+ENTRY(__bpon)
+	.globl __bpon
+	BPON
+	br	%r14
+
 /*
  * Scheduler resume function, called by switch_to
  *  gpr2 = (task_struct *) prev
@@ -234,7 +267,10 @@ ENTRY(sie64a)
 	jnz	.Lsie_skip
 	TSTMSK	__LC_CPU_FLAGS,_CIF_FPU
 	jo	.Lsie_skip			# exit if fp/vx regs changed
+	BPON
 	sie	0(%r14)
+.Lsie_exit:
+	BPOFF
 .Lsie_skip:
 	ni	__SIE_PROG0C+3(%r14),0xfe	# no longer in SIE
 	lctlg	%c1,%c1,__LC_USER_ASCE		# load primary asce
@@ -286,6 +322,7 @@ ENTRY(system_call)
 	stpt	__LC_SYNC_ENTER_TIMER
 .Lsysc_stmg:
 	stmg	%r8,%r15,__LC_SAVE_AREA_SYNC
+	BPOFF
 	lg	%r10,__LC_LAST_BREAK
 	lg	%r12,__LC_THREAD_INFO
 	lghi	%r14,_PIF_SYSCALL
@@ -332,6 +369,7 @@ ENTRY(system_call)
 	jnz	.Lsysc_work			# check for work
 	TSTMSK	__LC_CPU_FLAGS,_CIF_WORK
 	jnz	.Lsysc_work
+	BPON
 .Lsysc_restore:
 	lg	%r14,__LC_VDSO_PER_CPU
 	lmg	%r0,%r10,__PT_R0(%r11)
@@ -492,6 +530,7 @@ ENTRY(kernel_thread_starter)
 
 ENTRY(pgm_check_handler)
 	stpt	__LC_SYNC_ENTER_TIMER
+	BPOFF
 	stmg	%r8,%r15,__LC_SAVE_AREA_SYNC
 	lg	%r10,__LC_LAST_BREAK
 	lg	%r12,__LC_THREAD_INFO
@@ -590,6 +629,7 @@ ENTRY(pgm_check_handler)
 ENTRY(io_int_handler)
 	STCK	__LC_INT_CLOCK
 	stpt	__LC_ASYNC_ENTER_TIMER
+	BPOFF
 	stmg	%r8,%r15,__LC_SAVE_AREA_ASYNC
 	lg	%r10,__LC_LAST_BREAK
 	lg	%r12,__LC_THREAD_INFO
@@ -641,9 +681,13 @@ ENTRY(io_int_handler)
 	lg	%r14,__LC_VDSO_PER_CPU
 	lmg	%r0,%r10,__PT_R0(%r11)
 	mvc	__LC_RETURN_PSW(16),__PT_PSW(%r11)
+	tm	__PT_PSW+1(%r11),0x01	# returning to user ?
+	jno	.Lio_exit_kernel
+	BPON
 .Lio_exit_timer:
 	stpt	__LC_EXIT_TIMER
 	mvc	__VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER
+.Lio_exit_kernel:
 	lmg	%r11,%r15,__PT_R11(%r11)
 	lpswe	__LC_RETURN_PSW
 .Lio_done:
@@ -775,6 +819,7 @@ ENTRY(io_int_handler)
 ENTRY(ext_int_handler)
 	STCK	__LC_INT_CLOCK
 	stpt	__LC_ASYNC_ENTER_TIMER
+	BPOFF
 	stmg	%r8,%r15,__LC_SAVE_AREA_ASYNC
 	lg	%r10,__LC_LAST_BREAK
 	lg	%r12,__LC_THREAD_INFO
@@ -824,6 +869,7 @@ ENTRY(psw_idle)
 .Lpsw_idle_stcctm:
 #endif
 	oi	__LC_CPU_FLAGS+7,_CIF_ENABLED_WAIT
+	BPON
 	STCK	__CLOCK_IDLE_ENTER(%r2)
 	stpt	__TIMER_IDLE_ENTER(%r2)
 .Lpsw_idle_lpsw:
@@ -931,6 +977,7 @@ load_fpu_regs:
  */
 ENTRY(mcck_int_handler)
 	STCK	__LC_MCCK_CLOCK
+	BPOFF
 	la	%r1,4095		# revalidate r1
 	spt	__LC_CPU_TIMER_SAVE_AREA-4095(%r1)	# revalidate cpu timer
 	lmg	%r0,%r15,__LC_GPREGS_SAVE_AREA-4095(%r1)# revalidate gprs
@@ -997,6 +1044,7 @@ ENTRY(mcck_int_handler)
 	mvc	__LC_RETURN_MCCK_PSW(16),__PT_PSW(%r11) # move return PSW
 	tm	__LC_RETURN_MCCK_PSW+1,0x01 # returning to user ?
 	jno	0f
+	BPON
 	stpt	__LC_EXIT_TIMER
 	mvc	__VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER
 0:	lmg	%r11,%r15,__PT_R11(%r11)
--- a/arch/s390/kernel/ipl.c
+++ b/arch/s390/kernel/ipl.c
@@ -563,6 +563,7 @@ static struct kset *ipl_kset;
 
 static void __ipl_run(void *unused)
 {
+	__bpon();
 	diag308(DIAG308_LOAD_CLEAR, NULL);
 	if (MACHINE_IS_VM)
 		__cpcmd("IPL", NULL, 0, NULL);
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -304,6 +304,7 @@ static void pcpu_delegate(struct pcpu *p
 	mem_assign_absolute(lc->restart_fn, (unsigned long) func);
 	mem_assign_absolute(lc->restart_data, (unsigned long) data);
 	mem_assign_absolute(lc->restart_source, source_cpu);
+	__bpon();
 	asm volatile(
 		"0:	sigp	0,%0,%2	# sigp restart to target cpu\n"
 		"	brc	2,0b	# busy, try again\n"
@@ -877,6 +878,7 @@ void __cpu_die(unsigned int cpu)
 void __noreturn cpu_die(void)
 {
 	idle_task_exit();
+	__bpon();
 	pcpu_sigp_retry(pcpu_devices + smp_processor_id(), SIGP_STOP, 0);
 	for (;;) ;
 }

  parent reply	other threads:[~2018-04-27 15:14 UTC|newest]

Thread overview: 80+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-27 13:57 [PATCH 4.9 00/74] 4.9.97-stable review Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 4.9 01/74] cifs: do not allow creating sockets except with SMB1 posix exensions Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 4.9 02/74] x86/tsc: Prevent 32bit truncation in calc_hpet_ref() Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 4.9 03/74] drm/vc4: Fix memory leak during BO teardown Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 4.9 04/74] drm/i915: Fix LSPCON TMDS output buffer enabling from low-power state Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 4.9 05/74] i2c: i801: store and restore the SLVCMD register at load and unload Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 4.9 06/74] i2c: i801: Save register SMBSLVCMD value only once Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 4.9 07/74] i2c: i801: Restore configuration at shutdown Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 4.9 08/74] usb: musb: fix enumeration after resume Greg Kroah-Hartman
2018-04-27 13:57 ` [PATCH 4.9 09/74] usb: musb: call pm_runtime_{get,put}_sync before reading vbus registers Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 10/74] usb: musb: Fix external abort in musb_remove on omap2430 Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 11/74] MIPS: Generic: Fix big endian CPUs on generic machine Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 12/74] Input: drv260x - fix initializing overdrive voltage Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 13/74] power: supply: bq2415x: check for NULL acpi_id to avoid null pointer dereference Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 14/74] [media] stk-webcam: fix an endian bug in stk_camera_read_reg() Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 15/74] OF: Prevent unaligned access in of_alias_scan() Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 16/74] ath9k_hw: check if the chip failed to wake up Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 17/74] jbd2: fix use after free in kjournald2() Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 18/74] Revert "perf tools: Decompress kernel module when reading DSO data" Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 19/74] perf: Fix sample_max_stack maximum check Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 20/74] perf: Return proper values for user stack errors Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 21/74] RDMA/mlx5: Fix NULL dereference while accessing XRC_TGT QPs Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 22/74] drm/i915/bxt, glk: Increase PCODE timeouts during CDCLK freq changing Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 23/74] mac80211_hwsim: fix use-after-free bug in hwsim_exit_net Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 24/74] r8152: add Linksys USB3GIGV1 id Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 25/74] Revert "pinctrl: intel: Initialize GPIO properly when used through irqchip" Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 26/74] Revert "ath10k: send (re)assoc peer command when NSS changed" Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 27/74] PCI: Wait up to 60 seconds for device to become ready after FLR Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 28/74] s390: introduce CPU alternatives Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 29/74] s390: enable CPU alternatives unconditionally Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 30/74] KVM: s390: wire up bpb feature Greg Kroah-Hartman
2018-04-27 15:43   ` Christian Borntraeger
2018-04-27 13:58 ` [PATCH 4.9 31/74] s390: scrub registers on kernel entry and KVM exit Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 32/74] s390: add optimized array_index_mask_nospec Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 33/74] s390/alternative: use a copy of the facility bit mask Greg Kroah-Hartman
2018-04-27 13:58 ` Greg Kroah-Hartman [this message]
2018-04-27 13:58 ` [PATCH 4.9 35/74] s390: run user space and KVM guests with modified branch prediction Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 36/74] s390: introduce execute-trampolines for branches Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 37/74] KVM: s390: force bp isolation for VSIE Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 38/74] s390: Replace IS_ENABLED(EXPOLINE_*) with IS_ENABLED(CONFIG_EXPOLINE_*) Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 39/74] s390: do not bypass BPENTER for interrupt system calls Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 40/74] s390/entry.S: fix spurious zeroing of r0 Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 41/74] s390: move nobp parameter functions to nospec-branch.c Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 42/74] s390: add automatic detection of the spectre defense Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 43/74] s390: report spectre mitigation via syslog Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 44/74] s390: add sysfs attributes for spectre Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 45/74] s390: correct nospec auto detection init order Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 46/74] s390: correct module section names for expoline code revert Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 47/74] bonding: do not set slave_dev npinfo before slave_enable_netpoll in bond_enslave Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 48/74] KEYS: DNS: limit the length of option strings Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 49/74] l2tp: check sockaddr length in pppol2tp_connect() Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 50/74] net: validate attribute sizes in neigh_dump_table() Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 51/74] llc: delete timers synchronously in llc_sk_free() Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 52/74] tcp: dont read out-of-bounds opsize Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 53/74] team: avoid adding twice the same option to the event list Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 54/74] team: fix netconsole setup over team Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 55/74] packet: fix bitfield update race Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 56/74] tipc: add policy for TIPC_NLA_NET_ADDR Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 57/74] pppoe: check sockaddr length in pppoe_connect() Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 58/74] vlan: Fix reading memory beyond skb->tail in skb_vlan_tagged_multi Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 59/74] sctp: do not check port in sctp_inet6_cmp_addr Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 60/74] net: sched: ife: signal not finding metaid Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 61/74] llc: hold llc_sap before release_sock() Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 62/74] llc: fix NULL pointer deref for SOCK_ZAPPED Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 63/74] net: ethernet: ti: cpsw: fix tx vlan priority mapping Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 64/74] net: fix deadlock while clearing neighbor proxy table Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 65/74] tcp: md5: reject TCP_MD5SIG or TCP_MD5SIG_EXT on established sockets Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 66/74] net: af_packet: fix race in PACKET_{R|T}X_RING Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 67/74] ipv6: add RTA_TABLE and RTA_PREFSRC to rtm_ipv6_policy Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 68/74] strparser: Fix incorrect strp->need_bytes value Greg Kroah-Hartman
2018-04-27 13:58 ` [PATCH 4.9 69/74] scsi: mptsas: Disable WRITE SAME Greg Kroah-Hartman
2018-04-27 13:59 ` [PATCH 4.9 70/74] cdrom: information leak in cdrom_ioctl_media_changed() Greg Kroah-Hartman
2018-04-27 13:59 ` [PATCH 4.9 71/74] s390/cio: update chpid descriptor after resource accessibility event Greg Kroah-Hartman
2018-04-27 13:59 ` [PATCH 4.9 72/74] s390/dasd: fix IO error for newly defined devices Greg Kroah-Hartman
2018-04-27 13:59 ` [PATCH 4.9 73/74] s390/uprobes: implement arch_uretprobe_is_alive() Greg Kroah-Hartman
2018-04-27 13:59 ` [PATCH 4.9 74/74] ACPI / video: Only default only_lcd to true on Win8-ready _desktops_ Greg Kroah-Hartman
2018-04-27 18:13 ` [PATCH 4.9 00/74] 4.9.97-stable review Shuah Khan
2018-04-27 20:33 ` Dan Rue
2018-04-27 20:44 ` kernelci.org bot
2018-04-28 14:26 ` Guenter Roeck

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180427135711.344105030@linuxfoundation.org \
    --to=gregkh@linuxfoundation.org \
    --cc=cohuck@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=schwidefsky@de.ibm.com \
    --cc=stable@vger.kernel.org \
    --subject='Re: [PATCH 4.9 34/74] s390: add options to change branch prediction behaviour for the kernel' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).