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Date: Wed, 31 Oct 2012 08:55:54 +0000
From: "Jan Beulich" <JBeulich@...e.com>
To: "Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc: "xen-devel" <xen-devel@...ts.xen.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] xen/hypercall: fix hypercall fallback code for
very old hypervisors
>>> On 30.10.12 at 16:44, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> On Mon, Oct 29, 2012 at 10:08:17AM -0400, Konrad Rzeszutek Wilk wrote:
>> From: Jan Beulich <jbeulich@...e.com>
>>
>> While copying the argument structures in HYPERVISOR_event_channel_op()
>> and HYPERVISOR_physdev_op() into the local variable is sufficiently
>> safe even if the actual structure is smaller than the container one,
>> copying back eventual output values the same way isn't: This may
>> collide with on-stack variables (particularly "rc") which may change
>> between the first and second memcpy() (i.e. the second memcpy() could
>> discard that change).
>>
>> Move the fallback code into out-of-line functions, and handle all of
>> the operations known by this old a hypervisor individually: Some don't
>> require copying back anything at all, and for the rest use the
>> individual argument structures' sizes rather than the container's.
>>
>> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
>> Signed-off-by: Jan Beulich <jbeulich@...e.com>
>> [v2: Reduce #define/#undef usage in HYPERVISOR_physdev_op_compat().]
>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>
> And it looks like I get
>
> ERROR: "HYPERVISOR_event_channel_op_compat" [drivers/xen/xen-evtchn.ko]
> undefined!
>
> when I build xen-evtchn as module. Jan did you encounter this issue on
> 2.6.18?
No - the event channel driver there can't be built as a module, and
for the forward ported kernels I apparently never tried to build with
a compat setting of 3.0.2 or less (and I didn't care that much either
because the oldest we're actually concerned about is 3.0.4 to cover
some of those very old EC2 systems; I'll add the export at the right
point nevertheless).
Jan
>> ---
>> arch/x86/include/asm/xen/hypercall.h | 21 +++------
>> drivers/xen/Makefile | 2 +-
>> drivers/xen/fallback.c | 78
> ++++++++++++++++++++++++++++++++++
>> 3 files changed, 86 insertions(+), 15 deletions(-)
>> create mode 100644 drivers/xen/fallback.c
>>
>> diff --git a/arch/x86/include/asm/xen/hypercall.h
> b/arch/x86/include/asm/xen/hypercall.h
>> index 59c226d..c812360 100644
>> --- a/arch/x86/include/asm/xen/hypercall.h
>> +++ b/arch/x86/include/asm/xen/hypercall.h
>> @@ -359,18 +359,14 @@ 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);
>> }
>> +int __must_check HYPERVISOR_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)) {
>> - struct evtchn_op op;
>> - op.cmd = cmd;
>> - memcpy(&op.u, arg, sizeof(op.u));
>> - rc = _hypercall1(int, event_channel_op_compat, &op);
>> - memcpy(arg, &op.u, sizeof(op.u));
>> - }
>> + if (unlikely(rc == -ENOSYS))
>> + rc = HYPERVISOR_event_channel_op_compat(cmd, arg);
>> return rc;
>> }
>>
>> @@ -386,17 +382,14 @@ HYPERVISOR_console_io(int cmd, int count, char *str)
>> return _hypercall3(int, console_io, cmd, count, str);
>> }
>>
>> +int __must_check HYPERVISOR_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)) {
>> - struct physdev_op op;
>> - op.cmd = cmd;
>> - memcpy(&op.u, arg, sizeof(op.u));
>> - rc = _hypercall1(int, physdev_op_compat, &op);
>> - memcpy(arg, &op.u, sizeof(op.u));
>> - }
>> + if (unlikely(rc == -ENOSYS))
>> + rc = HYPERVISOR_physdev_op_compat(cmd, arg);
>> return rc;
>> }
>>
>> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
>> index 0e863703..46de6cd 100644
>> --- a/drivers/xen/Makefile
>> +++ b/drivers/xen/Makefile
>> @@ -2,7 +2,7 @@ ifneq ($(CONFIG_ARM),y)
>> obj-y += manage.o balloon.o
>> obj-$(CONFIG_HOTPLUG_CPU) += cpu_hotplug.o
>> endif
>> -obj-y += grant-table.o features.o events.o
>> +obj-y += grant-table.o features.o events.o fallback.o
>> obj-y += xenbus/
>>
>> nostackp := $(call cc-option, -fno-stack-protector)
>> diff --git a/drivers/xen/fallback.c b/drivers/xen/fallback.c
>> new file mode 100644
>> index 0000000..0bdc468
>> --- /dev/null
>> +++ b/drivers/xen/fallback.c
>> @@ -0,0 +1,78 @@
>> +#include <linux/kernel.h>
>> +#include <linux/string.h>
>> +#include <linux/bug.h>
>> +#include <asm/hypervisor.h>
>> +#include <asm/xen/hypercall.h>
>> +
>> +int HYPERVISOR_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;
>> +}
>> +
>> +int HYPERVISOR_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;
>> +}
>> --
>> 1.7.7.6
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