Re: [PATCH v6 10/34] x86, x86/mm, x86/xen, olpc: Use __va() against just the physical address in cr3

[Tom Lendacky]

On 6/7/2017 5:06 PM, Boris Ostrovsky wrote:
> On 06/07/2017 03:14 PM, Tom Lendacky wrote:
> > The cr3 register entry can contain the SME encryption bit that indicates
> > the PGD is encrypted.  The encryption bit should not be used when creating
> > a virtual address for the PGD table.
> >
> > Create a new function, read_cr3_pa(), that will extract the physical
> > address from the cr3 register. This function is then used where a virtual
> > address of the PGD needs to be created/used from the cr3 register.
> >
> > Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > ---
> >   arch/x86/include/asm/special_insns.h |    9 +++++++++
> >   arch/x86/kernel/head64.c             |    2 +-
> >   arch/x86/mm/fault.c                  |   10 +++++-----
> >   arch/x86/mm/ioremap.c                |    2 +-
> >   arch/x86/platform/olpc/olpc-xo1-pm.c |    2 +-
> >   arch/x86/power/hibernate_64.c        |    2 +-
> >   arch/x86/xen/mmu_pv.c                |    6 +++---
> >   7 files changed, 21 insertions(+), 12 deletions(-)

...

> > diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
> > index 1f386d7..2dc5243 100644
> > --- a/arch/x86/xen/mmu_pv.c
> > +++ b/arch/x86/xen/mmu_pv.c
> > @@ -2022,7 +2022,7 @@ static phys_addr_t __init xen_early_virt_to_phys(unsigned long vaddr)
> >   	pmd_t pmd;
> >   	pte_t pte;
> >   
> > -	pa = read_cr3();
> > +	pa = read_cr3_pa();
> >   	pgd = native_make_pgd(xen_read_phys_ulong(pa + pgd_index(vaddr) *
> >   						       sizeof(pgd)));
> >   	if (!pgd_present(pgd))
> > @@ -2102,7 +2102,7 @@ void __init xen_relocate_p2m(void)
> >   	pt_phys = pmd_phys + PFN_PHYS(n_pmd);
> >   	p2m_pfn = PFN_DOWN(pt_phys) + n_pt;
> >   
> > -	pgd = __va(read_cr3());
> > +	pgd = __va(read_cr3_pa());
> >   	new_p2m = (unsigned long *)(2 * PGDIR_SIZE);
> >   	idx_p4d = 0;
> >   	save_pud = n_pud;
> > @@ -2209,7 +2209,7 @@ static void __init xen_write_cr3_init(unsigned long cr3)
> >   {
> >   	unsigned long pfn = PFN_DOWN(__pa(swapper_pg_dir));
> >   
> > -	BUG_ON(read_cr3() != __pa(initial_page_table));
> > +	BUG_ON(read_cr3_pa() != __pa(initial_page_table));
> >   	BUG_ON(cr3 != __pa(swapper_pg_dir));
> >   
> >   	/*
>
>
> (Please copy Xen maintainers when modifying xen-related files.)

Sorry about that, missed adding the Xen maintainers when I added this
change.

> Given that page tables for Xen PV guests are controlled by the
> hypervisor I don't think this change (although harmless) is necessary.

I can back this change out if the Xen maintainers think that's best.

> What may be needed is making sure X86_FEATURE_SME is not set for PV guests.

And that may be something that Xen will need to control through either
CPUID or MSR support for the PV guests.

Thanks,
Tom

> -boris