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xen-devel
Re: [Xen-devel] a quick question about _PAGE_GLOBAL flag in para virt mo
weiming wrote:
Hi,
I noticed that in adjust_guest_l1e() in arch/x86/mm.c, _PAGE_GLOBAL
flag is set for guest's non-kernel pages. Meanwhile,
_PAGE_GUEST_KERNEL page cannot have the Global bit set.
What's the purpose of setting Global bit for guest's user pages?
AFAIK, when the Global bit is set, it prevents those entries be
flushed from TLB. So it makes more sense to set it for guest's kernel
pages.
In 64-bit, syscalls must go via Xen, which entails a cr3 reload. This
would normally flush the tlb, but since the usermode pages are global,
they remain in the tlb during the user->xen->kernel->xen->user transition.
J
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