On Wed, Jan 23, 2013 at 06:06:36PM +0800, Xiao Guangrong wrote:
> Introduce it to split the code of adjusting pte_access from the large
> function of set_spte
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 63 +++++++++++++++++++++++++++++++++-------------------
> 1 files changed, 40 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index af8bcb2..43b7e0c 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2324,25 +2324,18 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
> return 0;
> }
>
> -static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> - unsigned pte_access, int level,
> - gfn_t gfn, pfn_t pfn, bool speculative,
> - bool can_unsync, bool host_writable)
> +/*
> + * Return -1 if a race condition is detected, 1 if @gfn need to be
> + * write-protected, otherwise 0 is returned.
> + */
That's a little bit crafty.
Isn't it better to handle race condition in set_spte() explicitly?
Something like do:
if (host_writable && (pte_access & ACC_WRITE_MASK) &&
level > PT_PAGE_TABLE_LEVEL && has_wrprotected_page(vcpu->kvm, gfn, level))
return 0;
before calling vcpu_adjust_access() in set_spte()?
Or even do:
if ((pte_access & ACC_WRITE_MASK) && level > PT_PAGE_TABLE_LEVEL &&
has_wrprotected_page(vcpu->kvm, gfn, level))
return 0;
After calling vcpu_adjust_access().
The later will create read only large page mapping where now it is not
created, but it shouldn't be a problem as far as I see.
> +static int vcpu_adjust_access(struct kvm_vcpu *vcpu, u64 *sptep,
> + unsigned *pte_access, int level, gfn_t gfn,
> + bool can_unsync, bool host_writable)
> {
> - u64 spte;
> - int ret = 0;
> -
> - if (set_mmio_spte(sptep, gfn, pfn, pte_access))
> - return 0;
> + if (!host_writable)
> + *pte_access &= ~ACC_WRITE_MASK;
>
> - spte = PT_PRESENT_MASK;
> -
> - if (host_writable)
> - spte |= SPTE_HOST_WRITEABLE;
> - else
> - pte_access &= ~ACC_WRITE_MASK;
> -
> - if (pte_access & ACC_WRITE_MASK) {
> + if (*pte_access & ACC_WRITE_MASK) {
> /*
> * Other vcpu creates new sp in the window between
> * mapping_level() and acquiring mmu-lock. We can
> @@ -2351,7 +2344,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> */
> if (level > PT_PAGE_TABLE_LEVEL &&
> has_wrprotected_page(vcpu->kvm, gfn, level))
> - goto done;
> + return -1;
>
> /*
> * Optimization: for pte sync, if spte was writable the hash
> @@ -2360,17 +2353,41 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> * Same reasoning can be applied to dirty page accounting.
> */
> if (!can_unsync && is_writable_pte(*sptep))
> - goto out_access_adjust;
> + return 0;
>
> if (mmu_need_write_protect(vcpu, gfn, can_unsync)) {
> pgprintk("%s: found shadow page for %llx, marking ro\n",
> __func__, gfn);
> - ret = 1;
> - pte_access &= ~ACC_WRITE_MASK;
> +
> + *pte_access &= ~ACC_WRITE_MASK;
> + return 1;
> }
> }
>
> -out_access_adjust:
> + return 0;
> +}
> +
> +static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> + unsigned pte_access, int level,
> + gfn_t gfn, pfn_t pfn, bool speculative,
> + bool can_unsync, bool host_writable)
> +{
> + u64 spte;
> + int ret;
> +
> + if (set_mmio_spte(sptep, gfn, pfn, pte_access))
> + return 0;
> +
> + ret = vcpu_adjust_access(vcpu, sptep, &pte_access, level, gfn,
> + can_unsync, host_writable);
> + if (ret < 0)
> + return 0;
> +
> + spte = PT_PRESENT_MASK;
> +
> + if (host_writable)
> + spte |= SPTE_HOST_WRITEABLE;
> +
> if (!speculative)
> spte |= shadow_accessed_mask;
>
> @@ -2399,7 +2416,7 @@ out_access_adjust:
>
> if (mmu_spte_update(sptep, spte))
> kvm_flush_remote_tlbs(vcpu->kvm);
> -done:
> +
> return ret;
> }
>
> --
> 1.7.7.6
--
Gleb.
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