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    SubjectRe: [Xen-devel] [PATCH] PVH: vcpu info placement, load selectors, and remove debug printk.
    On Tue, 04 Jun 2013 09:27:03 +0100
    "Jan Beulich" <JBeulich@suse.com> wrote:

    > >>> On 04.06.13 at 02:43, Mukesh Rathor <mukesh.rathor@oracle.com>
    > >>> wrote:
    > > @@ -1327,6 +1329,18 @@ static void __init
    > > xen_setup_stackprotector(void) /* PVH TBD/FIXME: investigate
    > > setup_stack_canary_segment */ if
    > > (xen_feature(XENFEAT_auto_translated_physmap))
    > > { switch_to_new_gdt(0); +
    > > + /* xen started us with null selectors. load them
    > > now */
    > > + __asm__ __volatile__ (
    > > + "movl %0,%%ds\n"
    > > + "movl %0,%%ss\n"
    > > + "pushq %%rax\n"
    > > + "leaq 1f(%%rip),%%rax\n"
    > > + "pushq %%rax\n"
    > > + "retfq\n"
    > > + "1:\n"
    > > + : : "r" (__KERNEL_DS), "a" (__KERNEL_CS) :
    > > "memory"); +
    >
    > I can see why you want CS to be reloaded (and CS, other than the
    > comment says, clearly hasn't been holding a null selector up to here.
    >
    > I can't immediately see why you'd need SS to be other than null, and
    > it completely escapes me why you'd need to DS (but not ES) to be
    > non-null.
    >
    > Furthermore, is there any reason why you use "retfq" (Intel syntax)
    > when all assembly code otherwise uses AT&T syntax (the proper
    > equivalent here would be "lretq")?
    >
    > And finally, please consistently use %<number> (which, once
    > fixed, will make clear that the second constraint really can be "r"),
    > and avoid using suffixes on moves to/from selector registers
    > (which, once fixed, will make clear that at least the first constraint
    > really can be relaxed to "rm").

    Following OK? :

    if (xen_feature(XENFEAT_auto_translated_physmap)) {
    switch_to_new_gdt(0);

    asm volatile (
    "pushq %%rax\n"
    "leaq 1f(%%rip),%%rax\n"
    "pushq %%rax\n"
    "lretq\n"
    "1:\n"
    : : "a" (__KERNEL_CS) : "memory");

    return;
    }

    thanks,
    Mukesh



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