RE: [PATCH v2 15/15] Drivers: hv: Add modules to expose /dev/mshv to VMMs running on Hyper-V

[Saurabh Singh Sengar]

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> Subject: Re: [PATCH v2 15/15] Drivers: hv: Add modules to expose /dev/mshv
> to VMMs running on Hyper-V
> 
> On 8/18/2023 6:08 AM, Saurabh Singh Sengar wrote:
> >> +
> >> +config MSHV_VTL
> >> +	tristate "Microsoft Hyper-V VTL driver"
> >> +	depends on MSHV
> >> +	select HYPERV_VTL_MODE
> >> +	select TRANSPARENT_HUGEPAGE
> >
> > TRANSPARENT_HUGEPAGE can be avoided for now.
> >
> 
> I will remove it in the next version. Thanks.
> >> +
> >> +#define HV_GET_REGISTER_BATCH_SIZE	\
> >> +	(HV_HYP_PAGE_SIZE / sizeof(union hv_register_value))
> >> +#define HV_SET_REGISTER_BATCH_SIZE	\
> >> +	((HV_HYP_PAGE_SIZE - sizeof(struct hv_input_set_vp_registers)) \
> >> +		/ sizeof(struct hv_register_assoc))
> >> +
> >> +int hv_call_get_vp_registers(
> >> +		u32 vp_index,
> >> +		u64 partition_id,
> >> +		u16 count,
> >> +		union hv_input_vtl input_vtl,
> >> +		struct hv_register_assoc *registers) {
> >> +	struct hv_input_get_vp_registers *input_page;
> >> +	union hv_register_value *output_page;
> >> +	u16 completed = 0;
> >> +	unsigned long remaining = count;
> >> +	int rep_count, i;
> >> +	u64 status;
> >> +	unsigned long flags;
> >> +
> >> +	local_irq_save(flags);
> >> +
> >> +	input_page = *this_cpu_ptr(hyperv_pcpu_input_arg);
> >> +	output_page = *this_cpu_ptr(hyperv_pcpu_output_arg);
> >> +
> >> +	input_page->partition_id = partition_id;
> >> +	input_page->vp_index = vp_index;
> >> +	input_page->input_vtl.as_uint8 = input_vtl.as_uint8;
> >> +	input_page->rsvd_z8 = 0;
> >> +	input_page->rsvd_z16 = 0;
> >> +
> >> +	while (remaining) {
> >> +		rep_count = min(remaining, HV_GET_REGISTER_BATCH_SIZE);
> >> +		for (i = 0; i < rep_count; ++i)
> >> +			input_page->names[i] = registers[i].name;
> >> +
> >> +		status = hv_do_rep_hypercall(HVCALL_GET_VP_REGISTERS,
> >> rep_count,
> >> +					     0, input_page, output_page);
> >
> > Is there any possibility that count value is passed 0 by mistake ? In
> > that case status will remain uninitialized.
> >
> 
> These lines ensure rep_count is never 0 here:
> 
> 	while (remaining) {
> 		rep_count = min(remaining, HV_GET_REGISTER_BATCH_SIZE);
> 
> Remaining can't be 0 or the loop would exit, and
> HV_GET_REGISTER_BATCH_SIZE is not 0, or we would never get any registers.

There is a parameter in this function "count". I was checking if there is any possibility
that is passed as 0 by mistake ? this will lead to "remaining" value as 0 and loop will never
execute. Which results using "status" uninitialized later in the function.


> 
> >> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c index
> >> 13f972e72375..ccd76f30a638 100644
> >> --- a/drivers/hv/hv_common.c
> >> +++ b/drivers/hv/hv_common.c
> >> @@ -62,7 +62,11 @@ EXPORT_SYMBOL_GPL(hyperv_pcpu_output_arg);
> >>   */
> >>  static inline bool hv_output_arg_exists(void)  {
> >> +#ifdef CONFIG_MSHV_VTL
> >
> > Although today both the option works together. But thinking
> > which is more accurate CONFIG_HYPERV_VTL_MODE or
> > CONFIG_MSHV_VTL here for scalability of VTL modules.
> >
> 
> Good point. Though I'm not sure it matters too much right now,
> since as you mention they will always be enabled together.
> 
> Does CONFIG_HYPERV_VTL_MODE use the output arg?

Currently its not, I think MSHV_VTL is good for now. Thanks.

> 
> >> diff --git a/drivers/hv/mshv.h b/drivers/hv/mshv.h
> >> new file mode 100644
> >> index 000000000000..166480a73f3f
> >> --- /dev/null
> >> +++ b/drivers/hv/mshv.h
> >> @@ -0,0 +1,156 @@
> >> +/* SPDX-License-Identifier: GPL-2.0-only */
> >> +/*
> >> + * Copyright (c) 2023, Microsoft Corporation.
> >> + */
> >> +
> >> +#ifndef _MSHV_H_
> >> +#define _MSHV_H_
> >> +
> >> +#include <linux/spinlock.h>
> >> +#include <linux/mutex.h>
> >> +#include <linux/semaphore.h>
> >> +#include <linux/sched.h>
> >> +#include <linux/srcu.h>
> >> +#include <linux/wait.h>
> >> +#include <uapi/linux/mshv.h>
> >> +
> >> +/*
> >> + * Hyper-V hypercalls
> >> + */
> >> +
> >> +int hv_call_withdraw_memory(u64 count, int node, u64 partition_id);
> >> +int hv_call_create_partition(
> >> +		u64 flags,
> >> +		struct hv_partition_creation_properties creation_properties,
> >> +		union hv_partition_isolation_properties isolation_properties,
> >> +		u64 *partition_id);
> >> +int hv_call_initialize_partition(u64 partition_id);
> >> +int hv_call_finalize_partition(u64 partition_id);
> >> +int hv_call_delete_partition(u64 partition_id);
> >> +int hv_call_map_gpa_pages(
> >> +		u64 partition_id,
> >> +		u64 gpa_target,
> >> +		u64 page_count, u32 flags,
> >> +		struct page **pages);
> >> +int hv_call_unmap_gpa_pages(
> >> +		u64 partition_id,
> >> +		u64 gpa_target,
> >> +		u64 page_count, u32 flags);
> >> +int hv_call_get_vp_registers(
> >> +		u32 vp_index,
> >> +		u64 partition_id,
> >> +		u16 count,
> >> +		union hv_input_vtl input_vtl,
> >> +		struct hv_register_assoc *registers);
> >> +int hv_call_get_gpa_access_states(
> >> +		u64 partition_id,
> >> +		u32 count,
> >> +		u64 gpa_base_pfn,
> >> +		u64 state_flags,
> >> +		int *written_total,
> >> +		union hv_gpa_page_access_state *states);
> >> +
> >> +int hv_call_set_vp_registers(
> >> +		u32 vp_index,
> >> +		u64 partition_id,
> >> +		u16 count,
> >> +		union hv_input_vtl input_vtl,
> >> +		struct hv_register_assoc *registers);
> >
> > Nit: Opportunity to fix many of the checkpatch.pl related to line break here
> > and many other places.
> >
> 
> checkpatch.pl doesn't complain about anything in this file.

If we use --strict switch with checkpatch.pl we observe additional CHECK(s).
I observe 159 CHECK(s) with this patch overall.
(total: 1 errors, 7 warnings, 159 checks, 7460 lines checked)
Few examples:

CHECK: Lines should not end with a '('
#240: FILE: drivers/hv/hv_call.c:73:
+int hv_call_set_vp_registers(

CHECK: Alignment should match open parenthesis
#266: FILE: drivers/hv/hv_call.c:99:
+               memcpy(input_page->elements, registers,
+                       sizeof(struct hv_register_assoc) * rep_count);


I also see an error with flexible array, possibly we can fix that as well.

ERROR: Use C99 flexible arrays - see https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays
#7468: FILE: include/uapi/linux/mshv.h:134:
+       struct mshv_msi_routing_entry entries[0];
+};

- Saurabh