Re: [PATCH 2/2] Add MSR Bitmap support in VMX

[Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>]

On Thu, 2007-08-02 at 15:39 +0300, Avi Kivity wrote:
> He, Qing wrote:
> >>
> >> hmm.  While there's nothing wrong with the patch, there is a simpler way
> >> to do this:
> >>
> >>    static unsigned long vmx_msr_bitmap[PAGE_SIZE / sizeof(unsigned
> >> long)] __aligned(PAGE_SIZE);
> >>
> >> now there's no need to allocate, error-check, free, or kmap the memory.
> >> The io bitmaps can receive similar treatment.
> >>     
> >
> > Well, though not so important, kmapping do have a tiny advantage, it uses less virtual space if HIGHMEM is used. This makes sense when 1G limited kernel space is used, although it's highly unlikely to be a real problem.
> >
> >   
> 
> Starting a virtual machine consumes about 4MB of low memory for the
> shadow mmu (more for the memory map and for various slabs), so 4K is not
> an issue.
> 
> However, I do see an issue with my proposal. To get the physical address
> of the page, we need to use vmalloc_to_page(). But that won't work if
> kvm is built into the kernel (and thus uses large pages for data).
> 
> Rusty, what say you to a 'struct page *module_to_page(void *kaddr)'
> which does the right thing? Attached an implementation.

Hi Avi,

	Arch-specific, unfortunately: modules do not need to be allocated with
vmalloc (and for small modules probably shouldn't anyway).  Luckily
vmalloc always page-aligns AFAICT, so you get that.

So I think dynamic alloc is easier.
Rusty.





> 
> 


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