diff mbox series

[v3] xen: remove pre-xen3 fallback handlers

Message ID 20180313210652.3484599-1-arnd@arndb.de
State Superseded
Headers show
Series [v3] xen: remove pre-xen3 fallback handlers | expand

Commit Message

Arnd Bergmann March 13, 2018, 9:06 p.m. UTC 
The legacy hypercall handlers were originally added with
a comment explaining that "copying the argument structures in
HYPERVISOR_event_channel_op() and HYPERVISOR_physdev_op() into the local
variable is sufficiently safe" and only made sure to not write
past the end of the argument structure, the checks in linux/string.h
disagree with that, when link-time optimizations are used:

In function 'memcpy',
    inlined from 'pirq_query_unmask' at drivers/xen/fallback.c:53:2,
    inlined from '__startup_pirq' at drivers/xen/events/events_base.c:529:2,
    inlined from 'restore_pirqs' at drivers/xen/events/events_base.c:1439:3,
    inlined from 'xen_irq_resume' at drivers/xen/events/events_base.c:1581:2:
include/linux/string.h:350:3: error: call to '__read_overflow2' declared with attribute error: detected read beyond size of object passed as 2nd parameter
   __read_overflow2();
   ^

Further research turned out that only Xen 3.0.2 or earlier required the
fallback at all, while all versions in use today don't need it.
As far as I can tell, it is not even possible to run a mainline kernel
on those old Xen releases, at the time when they were in use, only
a patched kernel was supported anyway.

Fixes: cf47a83fb06e ("xen/hypercall: fix hypercall fallback code for very old hypervisors")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

---
[v2] use a table lookup instead of a switch/case statement, after
multiple suggestions.
[v3] remove that file completely
---
 arch/x86/include/asm/xen/hypercall.h | 13 +-----
 drivers/xen/Makefile                 |  1 -
 drivers/xen/fallback.c               | 81 ------------------------------------
 3 files changed, 2 insertions(+), 93 deletions(-)
 delete mode 100644 drivers/xen/fallback.c

-- 
2.9.0

Comments

Boris Ostrovsky March 14, 2018, 10:47 p.m. UTC | #1 
On 03/13/2018 05:06 PM, Arnd Bergmann wrote:
> The legacy hypercall handlers were originally added with

> a comment explaining that "copying the argument structures in

> HYPERVISOR_event_channel_op() and HYPERVISOR_physdev_op() into the local

> variable is sufficiently safe" and only made sure to not write

> past the end of the argument structure, the checks in linux/string.h

> disagree with that, when link-time optimizations are used:

>

> In function 'memcpy',

>     inlined from 'pirq_query_unmask' at drivers/xen/fallback.c:53:2,

>     inlined from '__startup_pirq' at drivers/xen/events/events_base.c:529:2,

>     inlined from 'restore_pirqs' at drivers/xen/events/events_base.c:1439:3,

>     inlined from 'xen_irq_resume' at drivers/xen/events/events_base.c:1581:2:

> include/linux/string.h:350:3: error: call to '__read_overflow2' declared with attribute error: detected read beyond size of object passed as 2nd parameter

>    __read_overflow2();

>    ^

>

> Further research turned out that only Xen 3.0.2 or earlier required the

> fallback at all, while all versions in use today don't need it.

> As far as I can tell, it is not even possible to run a mainline kernel

> on those old Xen releases, at the time when they were in use, only

> a patched kernel was supported anyway.

>

> Fixes: cf47a83fb06e ("xen/hypercall: fix hypercall fallback code for very old hypervisors")

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

> ---

> [v2] use a table lookup instead of a switch/case statement, after

> multiple suggestions.

> [v3] remove that file completely


(+Jan who added this file originally)

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Jan Beulich March 15, 2018, 8:24 a.m. UTC | #2 
>>> On 14.03.18 at 23:47, <boris.ostrovsky@oracle.com> wrote:

> On 03/13/2018 05:06 PM, Arnd Bergmann wrote:

>> The legacy hypercall handlers were originally added with

>> a comment explaining that "copying the argument structures in

>> HYPERVISOR_event_channel_op() and HYPERVISOR_physdev_op() into the local

>> variable is sufficiently safe" and only made sure to not write

>> past the end of the argument structure, the checks in linux/string.h

>> disagree with that, when link-time optimizations are used:

>>

>> In function 'memcpy',

>>     inlined from 'pirq_query_unmask' at drivers/xen/fallback.c:53:2,

>>     inlined from '__startup_pirq' at drivers/xen/events/events_base.c:529:2,

>>     inlined from 'restore_pirqs' at drivers/xen/events/events_base.c:1439:3,

>>     inlined from 'xen_irq_resume' at drivers/xen/events/events_base.c:1581:2:

>> include/linux/string.h:350:3: error: call to '__read_overflow2' declared with attribute error: detected read beyond size of object passed as 2nd parameter

>>    __read_overflow2();

>>    ^

>>

>> Further research turned out that only Xen 3.0.2 or earlier required the

>> fallback at all, while all versions in use today don't need it.

>> As far as I can tell, it is not even possible to run a mainline kernel

>> on those old Xen releases, at the time when they were in use, only

>> a patched kernel was supported anyway.

>>

>> Fixes: cf47a83fb06e ("xen/hypercall: fix hypercall fallback code for very old hypervisors")

>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

>> ---

>> [v2] use a table lookup instead of a switch/case statement, after

>> multiple suggestions.

>> [v3] remove that file completely

> 

> (+Jan who added this file originally)


Well, if everyone thinks backwards compatibility to those very old
hypervisors is not relevant anymore, then I'm not going to object.
It's really a matter of the consuming distros to know how far back
they want/need to guarantee compatibility.

Jan
diff mbox series

Patch

diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h
index bfd882617613..dcf9353a662a 100644
--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -365,15 +365,11 @@  HYPERVISOR_update_va_mapping(unsigned long va, pte_t new_val,
 		return _hypercall4(int, update_va_mapping, va,
 				   new_val.pte, new_val.pte >> 32, flags);
 }
-extern int __must_check xen_event_channel_op_compat(int, void *);
 
 static inline int
 HYPERVISOR_event_channel_op(int cmd, void *arg)
 {
-	int rc = _hypercall2(int, event_channel_op, cmd, arg);
-	if (unlikely(rc == -ENOSYS))
-		rc = xen_event_channel_op_compat(cmd, arg);
-	return rc;
+	return _hypercall2(int, event_channel_op, cmd, arg);
 }
 
 static inline int
@@ -388,15 +384,10 @@  HYPERVISOR_console_io(int cmd, int count, char *str)
 	return _hypercall3(int, console_io, cmd, count, str);
 }
 
-extern int __must_check xen_physdev_op_compat(int, void *);
-
 static inline int
 HYPERVISOR_physdev_op(int cmd, void *arg)
 {
-	int rc = _hypercall2(int, physdev_op, cmd, arg);
-	if (unlikely(rc == -ENOSYS))
-		rc = xen_physdev_op_compat(cmd, arg);
-	return rc;
+	return _hypercall2(int, physdev_op, cmd, arg);
 }
 
 static inline int
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 451e833f5931..ea2485069e19 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -1,6 +1,5 @@ 
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_HOTPLUG_CPU)		+= cpu_hotplug.o
-obj-$(CONFIG_X86)			+= fallback.o
 obj-y	+= grant-table.o features.o balloon.o manage.o preempt.o time.o
 obj-y	+= events/
 obj-y	+= xenbus/
diff --git a/drivers/xen/fallback.c b/drivers/xen/fallback.c
deleted file mode 100644
index b04fb64c5a91..000000000000
--- a/drivers/xen/fallback.c
+++ /dev/null
@@ -1,81 +0,0 @@ 
-#include <linux/kernel.h>
-#include <linux/string.h>
-#include <linux/bug.h>
-#include <linux/export.h>
-#include <asm/hypervisor.h>
-#include <asm/xen/hypercall.h>
-
-int xen_event_channel_op_compat(int cmd, void *arg)
-{
-	struct evtchn_op op;
-	int rc;
-
-	op.cmd = cmd;
-	memcpy(&op.u, arg, sizeof(op.u));
-	rc = _hypercall1(int, event_channel_op_compat, &op);
-
-	switch (cmd) {
-	case EVTCHNOP_close:
-	case EVTCHNOP_send:
-	case EVTCHNOP_bind_vcpu:
-	case EVTCHNOP_unmask:
-		/* no output */
-		break;
-
-#define COPY_BACK(eop) \
-	case EVTCHNOP_##eop: \
-		memcpy(arg, &op.u.eop, sizeof(op.u.eop)); \
-		break
-
-	COPY_BACK(bind_interdomain);
-	COPY_BACK(bind_virq);
-	COPY_BACK(bind_pirq);
-	COPY_BACK(status);
-	COPY_BACK(alloc_unbound);
-	COPY_BACK(bind_ipi);
-#undef COPY_BACK
-
-	default:
-		WARN_ON(rc != -ENOSYS);
-		break;
-	}
-
-	return rc;
-}
-EXPORT_SYMBOL_GPL(xen_event_channel_op_compat);
-
-int xen_physdev_op_compat(int cmd, void *arg)
-{
-	struct physdev_op op;
-	int rc;
-
-	op.cmd = cmd;
-	memcpy(&op.u, arg, sizeof(op.u));
-	rc = _hypercall1(int, physdev_op_compat, &op);
-
-	switch (cmd) {
-	case PHYSDEVOP_IRQ_UNMASK_NOTIFY:
-	case PHYSDEVOP_set_iopl:
-	case PHYSDEVOP_set_iobitmap:
-	case PHYSDEVOP_apic_write:
-		/* no output */
-		break;
-
-#define COPY_BACK(pop, fld) \
-	case PHYSDEVOP_##pop: \
-		memcpy(arg, &op.u.fld, sizeof(op.u.fld)); \
-		break
-
-	COPY_BACK(irq_status_query, irq_status_query);
-	COPY_BACK(apic_read, apic_op);
-	COPY_BACK(ASSIGN_VECTOR, irq_op);
-#undef COPY_BACK
-
-	default:
-		WARN_ON(rc != -ENOSYS);
-		break;
-	}
-
-	return rc;
-}
-EXPORT_SYMBOL_GPL(xen_physdev_op_compat);