On Thu, Sep 06, 2018 at 02:24:23PM +0200, Borislav Petkov wrote:
> On Thu, Sep 06, 2018 at 06:43:02AM -0500, Brijesh Singh wrote:
> > Currently, the per-cpu pvclock data is allocated dynamically when
> > cpu > HVC_BOOT_ARRAY_SIZE. The physical address of this variable is
> > shared between the guest and the hypervisor hence it must be mapped as
> > unencrypted (ie. C=0) when SEV is active.
> >
> > When SEV is active, we will be wasting fairly sizeable amount of memory
> > since each CPU will be doing a separate 4k allocation so that it can clear
> > C-bit. Let's define few extra static page sized array of pvclock data.
> > In the preparatory stage of CPU hotplug, use the element of this static
> > array to avoid the dynamic allocation. This array will be put in
> > the .data..decrypted section so that its mapped with C=0 during the boot.
> >
> > In non-SEV case, this static page will unused and free'd by the
> > free_decrypted_mem().
> >
> > Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> > Suggested-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> > Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > Cc: kvm@xxxxxxxxxxxxxxx
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> > Cc: kvm@xxxxxxxxxxxxxxx
> > Cc: "Radim Krčmář" <rkrcmar@xxxxxxxxxx>
> > ---
> > arch/x86/include/asm/mem_encrypt.h | 4 ++++
> > arch/x86/kernel/kvmclock.c | 22 +++++++++++++++++++---
> > arch/x86/kernel/vmlinux.lds.S | 3 +++
> > arch/x86/mm/init.c | 3 +++
> > arch/x86/mm/mem_encrypt.c | 10 ++++++++++
> > 5 files changed, 39 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> > index 802b2eb..aa204af 100644
> > --- a/arch/x86/include/asm/mem_encrypt.h
> > +++ b/arch/x86/include/asm/mem_encrypt.h
> > @@ -48,11 +48,13 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size);
> >
> > /* Architecture __weak replacement functions */
> > void __init mem_encrypt_init(void);
> > +void __init free_decrypted_mem(void);
> >
> > bool sme_active(void);
> > bool sev_active(void);
> >
> > #define __decrypted __attribute__((__section__(".data..decrypted")))
> > +#define __decrypted_hvclock __attribute__((__section__(".data..decrypted_hvclock")))
>
> So are we going to be defining a decrypted section for every piece of
> machinery now?
>
> That's a bit too much in my book.
>
> Why can't you simply free everything in .data..decrypted on !SVE guests?
That would prevent adding __decrypted to existing declarations, e.g.
hv_clock_boot, which would be ugly in its own right. A more generic
solution would be to add something like __decrypted_exclusive to mark
data that is used if and only if SEV is active, and then free the
SEV-only data when SEV is disabled.
Originally, my thought was that this would be a one-off case and the
array could be freed directly in kvmclock_init(), e.g.:
static struct pvclock_vsyscall_time_info
hv_clock_aux[HVC_AUX_ARRAY_SIZE] __decrypted __aligned(PAGE_SIZE);
...
void __init kvmclock_init(void)
{
u8 flags;
if (!sev_active())
free_init_pages("unused decrypted",
(unsigned long)hv_clock_aux,
(unsigned long)hv_clock_aux + sizeof(hv_clock_aux));
>
> --
> Regards/Gruss,
> Boris.
>
> SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
> --
