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    Subject[PATCH 02/33] KVM: MMU: emulated cmpxchg8b should be atomic on i386
    Date
    From: Marcelo Tosatti <marcelo@kvack.org>

    Emulate cmpxchg8b atomically on i386. This is required to avoid a guest
    pte walker from seeing a splitted write.

    [avi: make it compile]

    Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
    Signed-off-by: Avi Kivity <avi@qumranet.com>
    ---
    drivers/kvm/x86.c | 26 ++++++++++++++++++++++++++
    1 files changed, 26 insertions(+), 0 deletions(-)

    diff --git a/drivers/kvm/x86.c b/drivers/kvm/x86.c
    index 9db4e32..3b79684 100644
    --- a/drivers/kvm/x86.c
    +++ b/drivers/kvm/x86.c
    @@ -25,6 +25,7 @@
    #include <linux/vmalloc.h>
    #include <linux/module.h>
    #include <linux/mman.h>
    +#include <linux/highmem.h>

    #include <asm/uaccess.h>
    #include <asm/msr.h>
    @@ -1674,6 +1675,31 @@ static int emulator_cmpxchg_emulated(unsigned long addr,
    reported = 1;
    printk(KERN_WARNING "kvm: emulating exchange as write\n");
    }
    +#ifndef CONFIG_X86_64
    + /* guests cmpxchg8b have to be emulated atomically */
    + if (bytes == 8) {
    + gpa_t gpa = vcpu->mmu.gva_to_gpa(vcpu, addr);
    + struct page *page;
    + char *addr;
    + u64 val;
    +
    + if (gpa == UNMAPPED_GVA ||
    + (gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
    + goto emul_write;
    +
    + if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK))
    + goto emul_write;
    +
    + val = *(u64 *)new;
    + page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
    + addr = kmap_atomic(page, KM_USER0);
    + set_64bit((u64 *)(addr + offset_in_page(gpa)), val);
    + kunmap_atomic(addr, KM_USER0);
    + kvm_release_page_dirty(page);
    + }
    +emul_write:
    +#endif
    +
    return emulator_write_emulated(addr, new, bytes, vcpu);
    }

    --
    1.5.3.7


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