linux-kernel - Re: [PATCH v0 14/15] mshv: Remove mapping of mmio space during map user ioctl

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Message-ID: <f92a90d2-77e6-33cc-0c08-3851242298e0@linux.microsoft.com>
Date: Fri, 23 Jan 2026 18:12:14 -0800
From: Mukesh R <mrathor@...ux.microsoft.com>
To: Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
 linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
 linux-pci@...r.kernel.org, linux-arch@...r.kernel.org
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com, longli@...rosoft.com, catalin.marinas@....com,
 will@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, joro@...tes.org,
 lpieralisi@...nel.org, kwilczynski@...nel.org, mani@...nel.org,
 robh@...nel.org, bhelgaas@...gle.com, arnd@...db.de, mhklinux@...look.com,
 romank@...ux.microsoft.com
Subject: Re: [PATCH v0 14/15] mshv: Remove mapping of mmio space during map
 user ioctl

On 1/23/26 10:34, Nuno Das Neves wrote:
> On 1/19/2026 10:42 PM, Mukesh R wrote:
>> From: Mukesh Rathor <mrathor@...ux.microsoft.com>
>>
>> VFIO no longer puts the mmio pfn in vma->vm_pgoff. So, remove code
>> that is using it to map mmio space. It is broken and will cause
>> panic.
> 
> What is the reason for having this as a separate commit from patch 15?
> It seems like removing this code and adding the mmio intercept
> handling could be done in one patch.

Just ease of review and porting patches from this branch to that
branch to that release to this release... I am sure someone would
have asked for this to be a separate patch :).

Thanks,
-Mukesh


>>
>> Signed-off-by: Mukesh Rathor <mrathor@...ux.microsoft.com>
>> ---
>>   drivers/hv/mshv_root_main.c | 20 ++++----------------
>>   1 file changed, 4 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
>> index 27313419828d..03f3aa9f5541 100644
>> --- a/drivers/hv/mshv_root_main.c
>> +++ b/drivers/hv/mshv_root_main.c
>> @@ -1258,16 +1258,8 @@ static int mshv_prepare_pinned_region(struct mshv_mem_region *region)
>>   }
>>   
>>   /*
>> - * This maps two things: guest RAM and for pci passthru mmio space.
>> - *
>> - * mmio:
>> - *  - vfio overloads vm_pgoff to store the mmio start pfn/spa.
>> - *  - Two things need to happen for mapping mmio range:
>> - *	1. mapped in the uaddr so VMM can access it.
>> - *	2. mapped in the hwpt (gfn <-> mmio phys addr) so guest can access it.
>> - *
>> - *   This function takes care of the second. The first one is managed by vfio,
>> - *   and hence is taken care of via vfio_pci_mmap_fault().
>> + * This is called for both user ram and mmio space. The mmio space is not
>> + * mapped here, but later during intercept.
>>    */
>>   static long
>>   mshv_map_user_memory(struct mshv_partition *partition,
>> @@ -1276,7 +1268,6 @@ mshv_map_user_memory(struct mshv_partition *partition,
>>   	struct mshv_mem_region *region;
>>   	struct vm_area_struct *vma;
>>   	bool is_mmio;
>> -	ulong mmio_pfn;
>>   	long ret;
>>   
>>   	if (mem.flags & BIT(MSHV_SET_MEM_BIT_UNMAP) ||
>> @@ -1286,7 +1277,6 @@ mshv_map_user_memory(struct mshv_partition *partition,
>>   	mmap_read_lock(current->mm);
>>   	vma = vma_lookup(current->mm, mem.userspace_addr);
>>   	is_mmio = vma ? !!(vma->vm_flags & (VM_IO | VM_PFNMAP)) : 0;
>> -	mmio_pfn = is_mmio ? vma->vm_pgoff : 0;
>>   	mmap_read_unlock(current->mm);
>>   
>>   	if (!vma)
>> @@ -1313,10 +1303,8 @@ mshv_map_user_memory(struct mshv_partition *partition,
>>   					    HV_MAP_GPA_NO_ACCESS, NULL);
>>   		break;
>>   	case MSHV_REGION_TYPE_MMIO:
>> -		ret = hv_call_map_mmio_pages(partition->pt_id,
>> -					     region->start_gfn,
>> -					     mmio_pfn,
>> -					     region->nr_pages);
>> +		/* mmio mappings are handled later during intercepts */
>> +		ret = 0;
>>   		break;
>>   	}
>>   
>