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Re: [Xen-devel] [PATCH v2 1/4] x86/compat: Test whether guest has 32b shinfo instead of being a PV 32b domain

On 07/07/2015 05:11 AM, Jan Beulich wrote:
On 29.06.15 at 22:21, <boris.ostrovsky@xxxxxxxxxx> wrote:
In preparation for enabling 32-bit PVH guests replace a number of guest mode's
tests that assume a PV guest with has_32bit_shinfo() that can be applicable
both PV and PVH guests.
Apart from this apparently needing re-basing, I also think this should
be swapped with patch 2, as right now it doesn't make much sense to
distinguish the two checks.

@@ -737,7 +737,7 @@ int arch_set_info_guest(
/* The context is a compat-mode one if the target domain is compat-mode;
       * we expect the tools to DTRT even in compat-mode callers. */
-    compat = is_pv_32on64_domain(d);
+    compat = has_32bit_shinfo(d);
Furthermore, looking at uses like this, tying such decisions to the
shared info layout looks kind of odd. I think for documentation
purposes we may need a differently named alias.

Yes, it does look odd, which is why I was asking in another thread about having another field in domain structure (well, I was asking about replacing has_32bit_shinfo but I think I can see now that wouldn't be right).

Are you suggesting a new macro, e.g.
#define is_32b_mode(d)    ((d)->arch.has_32bit_shinfo)

or would it better to add new field? Or get_mode() hvm op, similar to set_mode(), which can look, say, at EFER?

@@ -1721,9 +1721,7 @@ unsigned long hypercall_create_continuation(
              curr->arch.hvm_vcpu.hcall_preempted = 1;
- if ( is_pv_vcpu(curr) ?
-             !is_pv_32bit_vcpu(curr) :
-             curr->arch.hvm_vcpu.hcall_64bit )
+        if ( !has_32bit_shinfo(curr->domain) )
This is not a valid replacement - hcall_64bit depends on the mode
the vCPU currently is in, while has_32bit_shinfo() doesn't.

Right, and I don't think this change is needed anyway since hvm_do_hypercall() will set hcall_64bit for PVH guests as well (when the guest is in 64-bit mode)

--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -496,7 +496,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
-        if ( !is_pv_32on64_domain(d) )
+        if ( !has_32bit_shinfo(d) )
              ret = copy_from_guest(c.nat, op->u.vcpucontext.ctxt, 1);
              ret = copy_from_guest(c.cmp,
@@ -902,7 +902,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
-        if ( !is_pv_32on64_domain(d) )
+        if ( !has_32bit_shinfo(d) )
              ret = copy_to_guest(op->u.vcpucontext.ctxt, c.nat, 1);
              ret = copy_to_guest(guest_handle_cast(op->u.vcpucontext.ctxt,
Where is it written down what format 32-bit PVH guests' vCPU
contexts get passed in? It would seem to me that it would be
rather more natural for them to use the 64-bit layout. Or else
how do you intend to suppress them being able to enter 64-bit

So why do we use the 'else' clause for 32b PV guests when they also use the same vcpu_guest_context_x86_32_t in libxc/xc_dom_x86.c:vcpu_x86_32()?


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