linux-kernel - RE: [PATCH 2/2] uio_hv_generic: Use correct size for interrupt and monitor pages

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Message-ID:
 <BN7PR02MB41484C3B916A6D1DA7297277D4B92@BN7PR02MB4148.namprd02.prod.outlook.com>
Date: Sun, 20 Apr 2025 23:58:44 +0000
From: Michael Kelley <mhklinux@...look.com>
To: "longli@...uxonhyperv.com" <longli@...uxonhyperv.com>, "K. Y. Srinivasan"
	<kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu
	<wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>, Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: Long Li <longli@...rosoft.com>, "stable@...r.kernel.org"
	<stable@...r.kernel.org>
Subject: RE: [PATCH 2/2] uio_hv_generic: Use correct size for interrupt and
 monitor pages

From: longli@...uxonhyperv.com <longli@...uxonhyperv.com>
> 
> Interrupt and monitor pages should be in Hyper-V page size (4k bytes).
> This can be different to the system page size.

I'm curious about this change. Since Patch 1 of the series changes
the allocations to be the full PAGE_SIZE, what does it mean to set
the mapping size to less than a full page (in the case PAGE_SIZE >
HV_HYP_PAGE_SIZE)? mmap can only map full PAGE_SIZE pages,
so uio_mmap() rounds up the INT_PAGE_MAP and MON_PAGE_MAP
sizes to PAGE_SIZE when checking the validity of the mmap
parameters.

The changes in this patch do ensure that the INT_PAGE_MAP and
MON_PAGE_MAP "maps" entries in sysfs always show the size as
4096 even if the full PAGE_SIZE is actually mapped, but I'm not sure
if that difference is good or bad.

Michael

> 
> Cc: stable@...r.kernel.org
> Fixes: 95096f2fbd10 ("uio-hv-generic: new userspace i/o driver for VMBus")
> Signed-off-by: Long Li <longli@...rosoft.com>
> ---
>  drivers/uio/uio_hv_generic.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/uio/uio_hv_generic.c b/drivers/uio/uio_hv_generic.c
> index 1b19b5647495..08385b04c4ab 100644
> --- a/drivers/uio/uio_hv_generic.c
> +++ b/drivers/uio/uio_hv_generic.c
> @@ -287,13 +287,13 @@ hv_uio_probe(struct hv_device *dev,
>  	pdata->info.mem[INT_PAGE_MAP].name = "int_page";
>  	pdata->info.mem[INT_PAGE_MAP].addr
>  		= (uintptr_t)vmbus_connection.int_page;
> -	pdata->info.mem[INT_PAGE_MAP].size = PAGE_SIZE;
> +	pdata->info.mem[INT_PAGE_MAP].size = HV_HYP_PAGE_SIZE;
>  	pdata->info.mem[INT_PAGE_MAP].memtype = UIO_MEM_LOGICAL;
> 
>  	pdata->info.mem[MON_PAGE_MAP].name = "monitor_page";
>  	pdata->info.mem[MON_PAGE_MAP].addr
>  		= (uintptr_t)vmbus_connection.monitor_pages[1];
> -	pdata->info.mem[MON_PAGE_MAP].size = PAGE_SIZE;
> +	pdata->info.mem[MON_PAGE_MAP].size = HV_HYP_PAGE_SIZE;
>  	pdata->info.mem[MON_PAGE_MAP].memtype = UIO_MEM_LOGICAL;
> 
>  	if (channel->device_id == HV_NIC) {
> --
> 2.34.1
>