Re: [Xen-devel] [PATCH] xen: support 52 bit physical addresses in pv guests

From: Boris Ostrovsky
Date: Thu Sep 21 2017 - 15:01:19 EST




On 09/21/2017 12:16 PM, Andrew Cooper wrote:
On 21/09/17 17:00, Boris Ostrovsky wrote:




Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
ÂÂ arch/x86/include/asm/xen/page.h | 11 ++++++++++-
ÂÂ arch/x86/xen/mmu_pv.cÂÂÂÂÂÂÂÂÂÂ |Â 4 ++--
ÂÂ 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/xen/page.h
b/arch/x86/include/asm/xen/page.h
index 07b6531813c4..bcb8b193c8d1 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -26,6 +26,15 @@ typedef struct xpaddr {
ÂÂÂÂÂÂ phys_addr_t paddr;
ÂÂ } xpaddr_t;
ÂÂ +#ifdef CONFIG_X86_64
+#define XEN_PHYSICAL_MASKÂÂÂ ((1UL << 52) - 1)


SME is not supported for PV guests but for consistency (and in case sme
bit somehow gets set)
#define XEN_PHYSICAL_MASKÂÂÂ __sme_clr(((1UL << 52) - 1))

Hmm, really? Shouldn't we rather add something like

BUG_ON(sme_active());

somewhere?

We can do that too.

Please don't do anything to cause Linux to crash if Xen is using SME itself, but leaving all of the PV guest unencrypted.

sme_active() returns true if the *guest* enables it.

Also, if the guest's memory is unencrypted, doesn't this mean that mfns that it sees (or, rather, ptes) will not have the SME bit set?

-boris