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From: Oleksandr <olekstysh@gmail.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: xen-devel@lists.xenproject.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
	Russell King <linux@armlinux.org.uk>,
	Julien Grall <julien@xen.org>
Subject: Re: [PATCH V2 2/4] arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT
Date: Thu, 11 Nov 2021 00:14:19 +0200	[thread overview]
Message-ID: <60cc5b07-5935-aa26-8690-353c779bbab5@gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.21.2110271754400.20134@sstabellini-ThinkPad-T480s>


On 28.10.21 04:28, Stefano Stabellini wrote:

Hi Stefano

I am sorry for the late response.

> On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>
>> Read the start address of the grant table space from DT
>> (region 0).
>>
>> This patch mostly restores behaviour before commit 3cf4095d7446
>> ("arm/xen: Use xen_xlate_map_ballooned_pages to setup grant table")
>> but trying not to break the ACPI support added after that commit.
>> So the patch touches DT part only and leaves the ACPI part with
>> xen_xlate_map_ballooned_pages().
>>
>> This is a preparation for using Xen extended region feature
>> where unused regions of guest physical address space (provided
>> by the hypervisor) will be used to create grant/foreign/whatever
>> mappings instead of wasting real RAM pages from the domain memory
>> for establishing these mappings.
>>
>> The immediate benefit of this change:
>> - Avoid superpage shattering in Xen P2M when establishing
>>    stage-2 mapping (GFN <-> MFN) for the grant table space
>> - Avoid wasting real RAM pages (reducing the amount of memory
>>    usuable) for mapping grant table space
>> - The grant table space is always mapped at the exact
>>    same place (region 0 is reserved for the grant table)
>>
>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>> ---
>> Changes RFC -> V2:
>>     - new patch
>> ---
>>   arch/arm/xen/enlighten.c | 32 +++++++++++++++++++++++++-------
>>   1 file changed, 25 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
>> index 7f1c106b..dea46ec 100644
>> --- a/arch/arm/xen/enlighten.c
>> +++ b/arch/arm/xen/enlighten.c
>> @@ -59,6 +59,9 @@ unsigned long xen_released_pages;
>>   struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS] __initdata;
>>   
>>   static __read_mostly unsigned int xen_events_irq;
>> +static phys_addr_t xen_grant_frames;
> __read_mostly

ok


>
>
>> +#define GRANT_TABLE_INDEX   0
>>   
>>   uint32_t xen_start_flags;
>>   EXPORT_SYMBOL(xen_start_flags);
>> @@ -303,6 +306,7 @@ static void __init xen_acpi_guest_init(void)
>>   static void __init xen_dt_guest_init(void)
>>   {
>>   	struct device_node *xen_node;
>> +	struct resource res;
>>   
>>   	xen_node = of_find_compatible_node(NULL, NULL, "xen,xen");
>>   	if (!xen_node) {
>> @@ -310,6 +314,12 @@ static void __init xen_dt_guest_init(void)
>>   		return;
>>   	}
>>   
>> +	if (of_address_to_resource(xen_node, GRANT_TABLE_INDEX, &res)) {
>> +		pr_err("Xen grant table region is not found\n");
>> +		return;
>> +	}
>> +	xen_grant_frames = res.start;
>> +
>>   	xen_events_irq = irq_of_parse_and_map(xen_node, 0);
>>   }
>>   
>> @@ -317,16 +327,20 @@ static int __init xen_guest_init(void)
>>   {
>>   	struct xen_add_to_physmap xatp;
>>   	struct shared_info *shared_info_page = NULL;
>> -	int cpu;
>> +	int rc, cpu;
>>   
>>   	if (!xen_domain())
>>   		return 0;
>>   
>>   	if (!acpi_disabled)
>>   		xen_acpi_guest_init();
>> -	else
>> +	else {
>>   		xen_dt_guest_init();
>>   
>> +		if (!xen_grant_frames)
>> +			return -ENODEV;
> maybe we can avoid this, see below
>
>
>> +	}
>> +
>>   	if (!xen_events_irq) {
>>   		pr_err("Xen event channel interrupt not found\n");
>>   		return -ENODEV;
>> @@ -370,12 +384,16 @@ static int __init xen_guest_init(void)
>>   	for_each_possible_cpu(cpu)
>>   		per_cpu(xen_vcpu_id, cpu) = cpu;
>>   
>> -	xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
>> -	if (xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
>> -					  &xen_auto_xlat_grant_frames.vaddr,
>> -					  xen_auto_xlat_grant_frames.count)) {
>> +	if (!acpi_disabled) {
> To make the code more resilient couldn't we do:
>
> if (!acpi_disabled || !xen_grant_frames) {
I think, we can.

On the one hand, indeed the code more resilient and less change.
 From the other hand if grant table region is not found then something 
weird happened as region 0 is always present in reg property if 
hypervisor node is exposed to the guest.
The behavior before commit 3cf4095d7446 ("arm/xen: Use 
xen_xlate_map_ballooned_pages to setup grant table") was exactly the 
same in the context of the failure if region wasn't found.

...

Well, if we want to make code more resilient, I will update. But, looks 
like we also need to switch actions in xen_dt_guest_init() in order to 
process xen_events_irq before xen_grant_frames, otherwise we may return 
after failing with region and end up not initializing xen_events_irq so 
xen_guest_init() will fail earlier than reaches that check.
What do you think?


>
>> +		xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
>> +		rc = xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
>> +										   &xen_auto_xlat_grant_frames.vaddr,
>> +										   xen_auto_xlat_grant_frames.count);
>> +	} else
>> +		rc = gnttab_setup_auto_xlat_frames(xen_grant_frames);
>> +	if (rc) {
>>   		free_percpu(xen_vcpu_info);
>> -		return -ENOMEM;
>> +		return rc;
>>   	}
>>   	gnttab_init();

-- 
Regards,

Oleksandr Tyshchenko



  reply	other threads:[~2021-11-10 22:15 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-26 16:05 [PATCH V2 0/4] xen: Add support of extended regions (safe ranges) on Arm Oleksandr Tyshchenko
2021-10-26 16:05 ` [PATCH V2 1/4] xen/unpopulated-alloc: Drop check for virt_addr_valid() in fill_list() Oleksandr Tyshchenko
2021-10-28 18:57   ` Boris Ostrovsky
2021-10-26 16:05 ` [PATCH V2 2/4] arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT Oleksandr Tyshchenko
2021-10-28  1:28   ` Stefano Stabellini
2021-11-10 22:14     ` Oleksandr [this message]
2021-11-19  0:32       ` Stefano Stabellini
2021-11-19 18:25         ` Oleksandr
2021-10-26 16:05 ` [PATCH V2 3/4] xen/unpopulated-alloc: Add mechanism to use Xen resource Oleksandr Tyshchenko
2021-10-28 16:37   ` Stefano Stabellini
2021-11-09 18:34     ` Oleksandr
2021-11-19  0:59       ` Stefano Stabellini
2021-11-19 18:18         ` Oleksandr
2021-11-20  2:19           ` Stefano Stabellini
2021-11-23 16:46             ` Oleksandr
2021-11-23 21:25               ` Stefano Stabellini
2021-11-24  9:33                 ` Oleksandr
2021-11-24  5:16               ` Juergen Gross
2021-11-24  9:37                 ` Oleksandr
2021-10-28 19:08   ` Boris Ostrovsky
2021-11-09 18:51     ` Oleksandr
2021-10-26 16:05 ` [PATCH V2 4/4] arm/xen: Read extended regions from DT and init " Oleksandr Tyshchenko
2021-10-28  1:40   ` Stefano Stabellini
2021-11-10 20:21     ` Oleksandr
2021-11-19  1:19       ` Stefano Stabellini
2021-11-19 20:23         ` Oleksandr
2021-11-20  2:36           ` Stefano Stabellini
2021-11-20 13:38             ` Oleksandr

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