diff mbox series

[v4,09/15] Drivers: hv: Introduce hv_output_arg_exists in hv_common.c

Message ID 1696010501-24584-10-git-send-email-nunodasneves@linux.microsoft.com
State New
Headers
Series Introduce /dev/mshv drivers |

Commit Message

Nuno Das Neves Sept. 29, 2023, 6:01 p.m. UTC 
  This is a more flexible approach for determining whether to allocate the
output page.

Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Acked-by: Wei Liu <wei.liu@kernel.org>
---
 drivers/hv/hv_common.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

Comments

Long Li Oct. 6, 2023, 6:13 p.m. UTC | #1 
> Subject: Re: [PATCH v4 09/15] Drivers: hv: Introduce hv_output_arg_exists in
> hv_common.c
> 
> On 10/2/2023 12:29 PM, Alex Ionescu wrote:
> > Hi Nuno,
> >
> > Is it possible to simply change to always allocating the output page?
> > For example, the output page could be needed in scenarios where Linux
> > is not running as the root partition, since certain hypercalls that a
> > guest can make will still require one (I realize that's not the case
> > _today_, but I don't believe this optimization buys much).
> 
> I agree - it would indeed simplify the code, and guests will probably make use of it
> sooner or later.
> 
> Happy to make that change if Hyper-V guest maintainers agree.
> Long, Dexuan, Michael, what do you think?

There is no use case as of today for guest VMs. And it allocates extra memory that are never used when running as guest VMs.

I suggest keep this code unchanged as is.

Thanks,
Long
diff mbox series

Patch

diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index 39077841d518..3f6f23e4c579 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -58,6 +58,14 @@  EXPORT_SYMBOL_GPL(hyperv_pcpu_input_arg);
 void * __percpu *hyperv_pcpu_output_arg;
 EXPORT_SYMBOL_GPL(hyperv_pcpu_output_arg);
 
+/*
+ * Determine whether output arg is needed
+ */
+static inline bool hv_output_arg_exists(void)
+{
+	return hv_root_partition ? true : false;
+}
+
 static void hv_kmsg_dump_unregister(void);
 
 static struct ctl_table_header *hv_ctl_table_hdr;
@@ -342,10 +350,12 @@  int __init hv_common_init(void)
 	hyperv_pcpu_input_arg = alloc_percpu(void  *);
 	BUG_ON(!hyperv_pcpu_input_arg);
 
-	/* Allocate the per-CPU state for output arg for root */
-	if (hv_root_partition) {
+	if (hv_output_arg_exists()) {
 		hyperv_pcpu_output_arg = alloc_percpu(void *);
 		BUG_ON(!hyperv_pcpu_output_arg);
+	}
+
+	if (hv_root_partition) {
 		hv_synic_eventring_tail = alloc_percpu(u8 *);
 		BUG_ON(hv_synic_eventring_tail == NULL);
 	}
@@ -375,7 +385,7 @@  int hv_common_cpu_init(unsigned int cpu)
 	u8 **synic_eventring_tail;
 	u64 msr_vp_index;
 	gfp_t flags;
-	int pgcount = hv_root_partition ? 2 : 1;
+	int pgcount = hv_output_arg_exists() ? 2 : 1;
 	void *mem;
 	int ret;
 
@@ -393,9 +403,12 @@  int hv_common_cpu_init(unsigned int cpu)
 		if (!mem)
 			return -ENOMEM;
 
-		if (hv_root_partition) {
+		if (hv_output_arg_exists()) {
 			outputarg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
 			*outputarg = (char *)mem + HV_HYP_PAGE_SIZE;
+		}
+
+		if (hv_root_partition) {
 			synic_eventring_tail = (u8 **)this_cpu_ptr(hv_synic_eventring_tail);
 			*synic_eventring_tail = kcalloc(HV_SYNIC_SINT_COUNT, sizeof(u8),
 							flags);