Re: [PATCH] KVM: arm/arm64: Properly check for MMIO regions

["Raslan, KarimAllah" <karahmed@amazon.de>]

On Fri, 2019-07-12 at 10:22 +0200, KarimAllah Ahmed wrote:
> Valid RAM can live outside kernel control (e.g. using "mem=" command-line
> parameter). This memory can still be used as valid guest memory for KVM. So
> ensure that we validate that this memory is definitely not "RAM" before
> assuming that it is an MMIO region.

This patch actually suffers from the same problem pointed out here:
https://lkml.org/lkml/2019/7/12/760

.. so I will need to rework them together.

> 
> One way to use memory outside kernel control is:
> 
> 1- Pass 'mem=' in the kernel command-line to limit the amount of memory managed
>    by the kernel.
> 2- Map this physical memory you want to give to the guest with:
>    mmap("/dev/mem", physical_address_offset, ..)
> 3- Use the user-space virtual address as the "userspace_addr" field in
>    KVM_SET_USER_MEMORY_REGION ioctl.
> 
> One of the limitations of the current /dev/mem for ARM is that it would map
> this memory as uncached without this patch:
> https://lkml.org/lkml/2019/7/11/684
> 
> This work is similar to the work done on x86 here:
> https://lkml.org/lkml/2019/1/31/933
> 
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Julien Thierry <julien.thierry@arm.com>
> Cc: Suzuki K Pouloze <suzuki.poulose@arm.com>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: kvmarm@lists.cs.columbia.edu
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
> ---
>  virt/kvm/arm/mmu.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 06180c9..2105134 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -8,6 +8,7 @@
>  #include <linux/kvm_host.h>
>  #include <linux/io.h>
>  #include <linux/hugetlb.h>
> +#include <linux/memblock.h>
>  #include <linux/sched/signal.h>
>  #include <trace/events/kvm.h>
>  #include <asm/pgalloc.h>
> @@ -89,7 +90,7 @@ static void kvm_flush_dcache_pud(struct kvm *kvm,
>  
>  static bool kvm_is_device_pfn(unsigned long pfn)
>  {
> -	return !pfn_valid(pfn);
> +	return !memblock_is_memory(__pfn_to_phys(pfn));
>  }
>  
>  /**
> @@ -949,6 +950,7 @@ static void stage2_unmap_memslot(struct kvm *kvm,
>  	do {
>  		struct vm_area_struct *vma = find_vma(current->mm, hva);
>  		hva_t vm_start, vm_end;
> +		gpa_t gpa;
>  
>  		if (!vma || vma->vm_start >= reg_end)
>  			break;
> @@ -959,11 +961,14 @@ static void stage2_unmap_memslot(struct kvm *kvm,
>  		vm_start = max(hva, vma->vm_start);
>  		vm_end = min(reg_end, vma->vm_end);
>  
> -		if (!(vma->vm_flags & VM_PFNMAP)) {
> -			gpa_t gpa = addr + (vm_start - memslot->userspace_addr);
> -			unmap_stage2_range(kvm, gpa, vm_end - vm_start);
> -		}
>  		hva = vm_end;
> +
> +		if ((vma->vm_flags & VM_PFNMAP) &&
> +		    !memblock_is_memory(__pfn_to_phys(vma->vm_pgoff)))
> +			continue;
> +
> +		gpa = addr + (vm_start - memslot->userspace_addr);
> +		unmap_stage2_range(kvm, gpa, vm_end - vm_start);
>  	} while (hva < reg_end);
>  }
>  
> @@ -2329,7 +2334,8 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  		vm_start = max(hva, vma->vm_start);
>  		vm_end = min(reg_end, vma->vm_end);
>  
> -		if (vma->vm_flags & VM_PFNMAP) {
> +		if ((vma->vm_flags & VM_PFNMAP) &&
> +		    !memblock_is_memory(__pfn_to_phys(vma->vm_pgoff))) {
>  			gpa_t gpa = mem->guest_phys_addr +
>  				    (vm_start - mem->userspace_addr);
>  			phys_addr_t pa;



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