[4.2.y-ckt stable] Patch "ARM/arm64: KVM: test properly for a PTE's uncachedness" has been added to staging queue

[Christoffer Dall]

On Thu, Jan 14, 2016 at 03:15:03PM -0800, Kamal Mostafa wrote:
> This is a note to let you know that I have just added a patch titled
> 
>     ARM/arm64: KVM: test properly for a PTE's uncachedness
> 
> to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
> which can be found at:
> 
>     http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue
> 
> This patch is scheduled to be released in version 4.2.8-ckt2.
> 
> If you, or anyone else, feels it should not be added to this tree, please 
> reply to this email.

This fix was incorrect and was subsequently updated by the following
commit in mainline:

0de58f8 (ARM/arm64: KVM: correct PTE uncachedness check, 2015-12-03)

That update should be applied along with this one.

Thanks,
-Christoffer

> 
> ---8<------------------------------------------------------------
> 
> From 6cbe0242b8048e540987f9da422f067af5cda6cb Mon Sep 17 00:00:00 2001
> From: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Date: Tue, 10 Nov 2015 15:11:20 +0100
> Subject: ARM/arm64: KVM: test properly for a PTE's uncachedness
> 
> commit e6fab54423450d699a09ec2b899473a541f61971 upstream.
> 
> The open coded tests for checking whether a PTE maps a page as
> uncached use a flawed '(pte_val(xxx) & CONST) != CONST' pattern,
> which is not guaranteed to work since the type of a mapping is
> not a set of mutually exclusive bits
> 
> For HYP mappings, the type is an index into the MAIR table (i.e, the
> index itself does not contain any information whatsoever about the
> type of the mapping), and for stage-2 mappings it is a bit field where
> normal memory and device types are defined as follows:
> 
>     #define MT_S2_NORMAL            0xf
>     #define MT_S2_DEVICE_nGnRE      0x1
> 
> I.e., masking *and* comparing with the latter matches on the former,
> and we have been getting lucky merely because the S2 device mappings
> also have the PTE_UXN bit set, or we would misidentify memory mappings
> as device mappings.
> 
> Since the unmap_range() code path (which contains one instance of the
> flawed test) is used both for HYP mappings and stage-2 mappings, and
> considering the difference between the two, it is non-trivial to fix
> this by rewriting the tests in place, as it would involve passing
> down the type of mapping through all the functions.
> 
> However, since HYP mappings and stage-2 mappings both deal with host
> physical addresses, we can simply check whether the mapping is backed
> by memory that is managed by the host kernel, and only perform the
> D-cache maintenance if this is the case.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Tested-by: Pavel Fedin <p.fedin at samsung.com>
> Reviewed-by: Christoffer Dall <christoffer.dall at linaro.org>
> Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
> Signed-off-by: Kamal Mostafa <kamal at canonical.com>
> ---
>  arch/arm/kvm/mmu.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 6984342..7dace90 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -98,6 +98,11 @@ static void kvm_flush_dcache_pud(pud_t pud)
>  	__kvm_flush_dcache_pud(pud);
>  }
> 
> +static bool kvm_is_device_pfn(unsigned long pfn)
> +{
> +	return !pfn_valid(pfn);
> +}
> +
>  /**
>   * stage2_dissolve_pmd() - clear and flush huge PMD entry
>   * @kvm:	pointer to kvm structure.
> @@ -213,7 +218,7 @@ static void unmap_ptes(struct kvm *kvm, pmd_t *pmd,
>  			kvm_tlb_flush_vmid_ipa(kvm, addr);
> 
>  			/* No need to invalidate the cache for device mappings */
> -			if ((pte_val(old_pte) & PAGE_S2_DEVICE) != PAGE_S2_DEVICE)
> +			if (!kvm_is_device_pfn(__phys_to_pfn(addr)))
>  				kvm_flush_dcache_pte(old_pte);
> 
>  			put_page(virt_to_page(pte));
> @@ -305,8 +310,7 @@ static void stage2_flush_ptes(struct kvm *kvm, pmd_t *pmd,
> 
>  	pte = pte_offset_kernel(pmd, addr);
>  	do {
> -		if (!pte_none(*pte) &&
> -		    (pte_val(*pte) & PAGE_S2_DEVICE) != PAGE_S2_DEVICE)
> +		if (!pte_none(*pte) && !kvm_is_device_pfn(__phys_to_pfn(addr)))
>  			kvm_flush_dcache_pte(*pte);
>  	} while (pte++, addr += PAGE_SIZE, addr != end);
>  }
> @@ -1037,11 +1041,6 @@ static bool kvm_is_write_fault(struct kvm_vcpu *vcpu)
>  	return kvm_vcpu_dabt_iswrite(vcpu);
>  }
> 
> -static bool kvm_is_device_pfn(unsigned long pfn)
> -{
> -	return !pfn_valid(pfn);
> -}
> -
>  /**
>   * stage2_wp_ptes - write protect PMD range
>   * @pmd:	pointer to pmd entry
> --
> 1.9.1
>