Re: [RFC PATCH 6/6] KVM: SVM: Pin SEV pages in MMU during sev_launch_update_data()

[Maciej S. Szmigiero]

On 18.01.2022 16:00, Maciej S. Szmigiero wrote:
> Hi Nikunj,
>
> On 18.01.2022 12:06, Nikunj A Dadhania wrote:
> > From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> >
> > Pin the memory for the data being passed to launch_update_data()
> > because it gets encrypted before the guest is first run and must
> > not be moved which would corrupt it.
> >
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> > [ * Changed hva_to_gva() to take an extra argument and return gpa_t.
> >    * Updated sev_pin_memory_in_mmu() error handling.
> >    * As pinning/unpining pages is handled within MMU, removed
> >      {get,put}_user(). ]
> > Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
> > ---
> >   arch/x86/kvm/svm/sev.c | 122 ++++++++++++++++++++++++++++++++++++++++-
> >   1 file changed, 119 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index 14aeccfc500b..1ae714e83a3c 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> > @@ -22,6 +22,7 @@
> >   #include <asm/trapnr.h>
> >   #include <asm/fpu/xcr.h>
> > +#include "mmu.h"
> >   #include "x86.h"
> >   #include "svm.h"
> >   #include "svm_ops.h"
> > @@ -490,6 +491,110 @@ static unsigned long get_num_contig_pages(unsigned long idx,
> >       return pages;
> >   }
> > +#define SEV_PFERR_RO (PFERR_USER_MASK)
> > +#define SEV_PFERR_RW (PFERR_WRITE_MASK | PFERR_USER_MASK)
> > +
> > +static struct kvm_memory_slot *hva_to_memslot(struct kvm *kvm,
> > +                          unsigned long hva)
> > +{
> > +    struct kvm_memslots *slots = kvm_memslots(kvm);
> > +    struct kvm_memory_slot *memslot;
> > +    int bkt;
> > +
> > +    kvm_for_each_memslot(memslot, bkt, slots) {
> > +        if (hva >= memslot->userspace_addr &&
> > +            hva < memslot->userspace_addr +
> > +            (memslot->npages << PAGE_SHIFT))
> > +            return memslot;
> > +    }
> > +
> > +    return NULL;
> > +}
>
> We have kvm_for_each_memslot_in_hva_range() now, please don't do a linear
> search through memslots.
> You might need to move the aforementioned macro from kvm_main.c to some
> header file, though.

Besides performance considerations I can't see the code here taking into
account the fact that a hva can map to multiple memslots (they an overlap
in the host address space).

Thanks,
Maciej