linux-kernel - Re: [PATCH] KVM: SVM: Change flag passed to GUP fast in sev_pin

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Date:   Thu, 23 Apr 2020 13:34:24 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Janakarajan Natarajan <Janakarajan.Natarajan@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Mike Marshall <hubcap@...ibond.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH] KVM: SVM: Change flag passed to GUP fast in
 sev_pin_memory()

On Thu, Apr 23, 2020 at 10:24:19AM -0500, Janakarajan Natarajan wrote:
> When trying to lock read-only pages, sev_pin_memory() fails because FOLL_WRITE
> is used as the flag for get_user_pages_fast().
> 
> Commit 73b0140bf0fe ("mm/gup: change GUP fast to use flags rather than a write
> 'bool'") updated the get_user_pages_fast() call sites to use flags, but
> incorrectly updated the call in sev_pin_memory(). As the original coding of this
> call was correct, revert the change made by that commit.
> 
> Fixes: 73b0140bf0fe ("mm/gup: change GUP fast to use flags rather than a write 'bool'")
> Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@....com>

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> ---
>  arch/x86/kvm/svm/sev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index cf912b4aaba8..89f7f3aebd31 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -345,7 +345,7 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
>  		return NULL;
>  
>  	/* Pin the user virtual address. */
> -	npinned = get_user_pages_fast(uaddr, npages, FOLL_WRITE, pages);
> +	npinned = get_user_pages_fast(uaddr, npages, write ? FOLL_WRITE : 0, pages);
>  	if (npinned != npages) {
>  		pr_err("SEV: Failure locking %lu pages.\n", npages);
>  		goto err;
> -- 
> 2.17.1
>