Hi,
At 10:48 +0800 on 05 Dec (1196851700), Xin, Xiaohui wrote:
> The patch will check if the data guest writes to the page table contains
> valid mfn or not, if not, we believe it is a data page now and then
> unshadow the page.
Good plan, thanks.
> +static inline void
> +check_for_data_page_unshadow(struct vcpu *v, void *addr,mfn_t mfn)
> +{
> + gfn_t gfn;
> + p2m_type_t p2m_type;
> +
> +#if SHADOW_OPTIMIZATIONS & SHOPT_EARLY_UNSHADOW
> + if ( mfn_to_page(mfn)->shadow_flags & SHF_L2_32 )
> + {
> + gfn = _gfn((paddr_t)(((*(u32*)addr) & (PADDR_MASK&PAGE_MASK))) >>
> + PAGE_SHIFT);
Shouldn't you also check for the _PAGE_PRESENT bit? Otherwise I think
normal shadow performance could be hurt.
> + if ( gfn_to_mfn(v->domain, gfn, &p2m_type) == INVALID_MFN )
> + sh_remove_shadows(v, mfn, 1, 0);
> + }
> + else if (mfn_to_page(mfn)->shadow_flags &
> + (SHF_L4_64|SHF_L2_PAE|SHF_L2H_PAE))
Why not SHF_L3_64, SHF_l2_64 and SHF_L2H_64?
> + {
> + gfn = _gfn((paddr_t)(((*(u64*)addr) & (PADDR_MASK&PAGE_MASK))) >>
> + PAGE_SHIFT);
> + if ( gfn_to_mfn(v->domain, gfn, &p2m_type) == INVALID_MFN )
> + sh_remove_shadows(v, mfn, 1, 0);
> + }
> +#endif
> +}
>
> int
> sh_x86_emulate_write(struct vcpu *v, unsigned long vaddr, void *src,
> @@ -4068,7 +4092,8 @@ sh_x86_emulate_write(struct vcpu *v, uns
> check_for_early_unshadow(v, mfn);
> else
> reset_early_unshadow(v);
> -
> +
> + check_for_data_page_unshadow(v, addr, mfn);
> paging_mark_dirty(v->domain, mfn_x(mfn));
This, and its equivalent in sh_x86_emulate_cmpxchg, need to be gated on
bytes() being greater than the size of the read you'll be doing in
check_for_data_page_unshadow() or you'll get #PF when a guest writes to
the top word of a page.
Cheers,
Tim.
--
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems.
[Company #5334508: XenSource UK Ltd, reg'd c/o EC2Y 5EB, UK.]
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