Re: [PATCH v2 4.19 3/3] KVM: Use kvm_pfn_t for local PFN variable in hva_to_pfn_remapped()

[Paolo Bonzini <pbonzini@redhat.com>]

On 27/07/21 10:29, Ovidiu Panait wrote:
> From: Sean Christopherson <seanjc@google.com>
> 
> commit a9545779ee9e9e103648f6f2552e73cfe808d0f4 upstream
> 
> Use kvm_pfn_t, a.k.a. u64, for the local 'pfn' variable when retrieving
> a so called "remapped" hva/pfn pair.  In theory, the hva could resolve to
> a pfn in high memory on a 32-bit kernel.
> 
> This bug was inadvertantly exposed by commit bd2fae8da794 ("KVM: do not
> assume PTE is writable after follow_pfn"), which added an error PFN value
> to the mix, causing gcc to comlain about overflowing the unsigned long.
> 
>    arch/x86/kvm/../../../virt/kvm/kvm_main.c: In function ‘hva_to_pfn_remapped’:
>    include/linux/kvm_host.h:89:30: error: conversion from ‘long long unsigned int’
>                                    to ‘long unsigned int’ changes value from
>                                    ‘9218868437227405314’ to ‘2’ [-Werror=overflow]
>     89 | #define KVM_PFN_ERR_RO_FAULT (KVM_PFN_ERR_MASK + 2)
>        |                              ^
> virt/kvm/kvm_main.c:1935:9: note: in expansion of macro ‘KVM_PFN_ERR_RO_FAULT’
> 
> Cc: stable@vger.kernel.org
> Fixes: add6a0cd1c5b ("KVM: MMU: try to fix up page faults before giving up")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Message-Id: <20210208201940.1258328-1-seanjc@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
> ---
>   virt/kvm/kvm_main.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 3559eba5f502..a3d82113ae1c 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1501,7 +1501,7 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma,
>   			       bool write_fault, bool *writable,
>   			       kvm_pfn_t *p_pfn)
>   {
> -	unsigned long pfn;
> +	kvm_pfn_t pfn;
>   	pte_t *ptep;
>   	spinlock_t *ptl;
>   	int r;
> 

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

and the other two are the same as v1.

Paolo