Ingo Molnar wrote:
> Subject: [patch] KVM: paravirtual guest support
> From: Ingo Molnar <[EMAIL PROTECTED]>
>
> this enables a CONFIG_PARAVIRT Linux guest kernel to establish a
> hypercall API to a KVM host. If successfully registered, then the Linux
> guest will optimize a few things like its interrupt controller, io-delay
> and it also registers its cr3-cache structures with the host. (but the
> host will not touch those, just yet)
>
> (this is fully backwards compatible - if the WRMSR fails then the Linux
> guest continues to execute as a native kernel.)
>
> Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]>
> ---
> + /*
> + * Cache-hit: we load the cached host-CR3 value.
> + * This never causes any VM exit. (if it does then the
> + * hypervisor could do nothing with this instruction
> + * and the guest OS would be aborted)
> + */
> + asm volatile("movl %0, %%cr3"
> + : : "r" (cache->entry[idx].host_cr3));
> + goto out;
> + }
> + }
> +
> + /*
> + * Cache-miss. Load the guest-cr3 value into cr3, which will
> + * cause a VM exit to the hypervisor, which then loads the
> + * host cr3 value and updates the cr3_cache.
> + */
> + asm volatile("movl %0, %%cr3" : : "r" (guest_cr3));
> +out:
> + put_cpu_var(para_state);
> +}
> +
>
There's a problem here. A cache-hit cr3 is an hpa, while a cache-miss
cr3 is a gpa. The two could alias:
/* pseudoassembler */
guest:
mov $0x1234, %cr3 /* cache miss */
host:
creates shadow for 0x1234 at 0x5678
set cr3 cache entry: $0x1234 -> 0x5678
guest:
mov $0x5678, %cr3 /* cache miss */
vmx accepts that as a cached cr3 equivalent to the guest's 0x1234,
whereas a 0x5678 gpa cr3 was intended.
The only solution I see is to use the hypercall API on a cache miss.
Once the guest indicates it wants to use the cr3 cache, set_cr3() should
fault, and cr3 should only be accepted from the hypercall.
--
error compiling committee.c: too many arguments to function
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