linux-kernel - Re: [PATCH 2/5] x86/sgx: use VM_ACCESS

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Date:   Sun, 23 Oct 2022 23:09:24 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-sgx@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 2/5] x86/sgx: use VM_ACCESS_FLAGS

On Sun, Oct 23, 2022 at 11:07:47PM +0300, Jarkko Sakkinen wrote:
> On Wed, Oct 19, 2022 at 11:49:42AM +0800, Kefeng Wang wrote:
> > Simplify VM_READ|VM_WRITE|VM_EXEC with VM_ACCESS_FLAGS.
> > 
> > Cc: Jarkko Sakkinen <jarkko@...nel.org>
> > Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> > ---
> >  arch/x86/kernel/cpu/sgx/encl.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> > index 1ec20807de1e..6225c525372d 100644
> > --- a/arch/x86/kernel/cpu/sgx/encl.c
> > +++ b/arch/x86/kernel/cpu/sgx/encl.c
> > @@ -268,7 +268,7 @@ static struct sgx_encl_page *sgx_encl_load_page_in_vma(struct sgx_encl *encl,
> >  						       unsigned long addr,
> >  						       unsigned long vm_flags)
> >  {
> > -	unsigned long vm_prot_bits = vm_flags & (VM_READ | VM_WRITE | VM_EXEC);
> > +	unsigned long vm_prot_bits = vm_flags & VM_ACCESS_FLAGS;
> >  	struct sgx_encl_page *entry;
> >  
> >  	entry = xa_load(&encl->page_array, PFN_DOWN(addr));
> > @@ -502,7 +502,7 @@ static void sgx_vma_open(struct vm_area_struct *vma)
> >  int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start,
> >  		     unsigned long end, unsigned long vm_flags)
> >  {
> > -	unsigned long vm_prot_bits = vm_flags & (VM_READ | VM_WRITE | VM_EXEC);
> > +	unsigned long vm_prot_bits = vm_flags & VM_ACCESS_FLAGS;
> >  	struct sgx_encl_page *page;
> >  	unsigned long count = 0;
> >  	int ret = 0;
> > -- 
> > 2.35.3
> > 
> 
> Why?

Only benefit I see is a downside: you have xref VM_ACCESS_FLAGS, which
is counter-productive. Zero gain.

BR, Jarkko