On Thu, Jan 08, 2015 at 11:59:08AM +0000, Marc Zyngier wrote:
> Let's assume a guest has created an uncached mapping, and written
> to that page. Let's also assume that the host uses a cache-coherent
> IO subsystem. Let's finally assume that the host is under memory
> pressure and starts to swap things out.
>
> Before this "uncached" page is evicted, we need to make sure it
> gets invalidated, or the IO subsystem is going to swap out the
> cached view, loosing the data that has been written there.
>
> Signed-off-by: Marc Zyngier <[email protected]>
> ---
> arch/arm/include/asm/kvm_mmu.h | 31 +++++++++++++++++++++++++++
> arch/arm/kvm/mmu.c | 46
> +++++++++++++++++++++++++++-------------
> arch/arm64/include/asm/kvm_mmu.h | 18 ++++++++++++++++
> 3 files changed, 80 insertions(+), 15 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> index 63e0ecc..7ceb836 100644
> --- a/arch/arm/include/asm/kvm_mmu.h
> +++ b/arch/arm/include/asm/kvm_mmu.h
> @@ -44,6 +44,7 @@
>
> #ifndef __ASSEMBLY__
>
> +#include <linux/highmem.h>
> #include <asm/cacheflush.h>
> #include <asm/pgalloc.h>
>
> @@ -190,6 +191,36 @@ static inline void coherent_cache_guest_page(struct
> kvm_vcpu *vcpu, hva_t hva,
>
> #define kvm_virt_to_phys(x) virt_to_idmap((unsigned long)(x))
>
> +static inline void __kvm_flush_dcache_pte(pte_t pte)
> +{
> + void *va = kmap_atomic(pte_page(pte));
> +
> + kvm_flush_dcache_to_poc(va, PAGE_SIZE);
> +
> + kunmap_atomic(va);
> +}
> +
> +static inline void __kvm_flush_dcache_pmd(pmd_t pmd)
> +{
> + unsigned long size = PMD_SIZE;
> + pfn_t pfn = pmd_pfn(pmd);
> +
> + while (size) {
> + void *va = kmap_atomic_pfn(pfn);
> +
> + kvm_flush_dcache_to_poc(va, PAGE_SIZE);
> +
> + pfn++;
> + size -= PAGE_SIZE;
> +
> + kunmap_atomic(va);
> + }
> +}
> +
> +static inline void __kvm_flush_dcache_pud(pud_t pud)
> +{
> +}
> +
> void stage2_flush_vm(struct kvm *kvm);
>
> #endif /* !__ASSEMBLY__ */
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 1dc9778..1f5b793 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -58,6 +58,21 @@ static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm,
> phys_addr_t ipa)
> kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, kvm, ipa);
> }
>
> +static void kvm_flush_dcache_pte(pte_t pte)
> +{
> + __kvm_flush_dcache_pte(pte);
> +}
> +
> +static void kvm_flush_dcache_pmd(pmd_t pmd)
> +{
> + __kvm_flush_dcache_pmd(pmd);
> +}
> +
> +static void kvm_flush_dcache_pud(pud_t pud)
> +{
> + __kvm_flush_dcache_pud(pud);
> +}
> +
> static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
> int min, int max)
> {
> @@ -128,9 +143,12 @@ static void unmap_ptes(struct kvm *kvm, pmd_t *pmd,
> start_pte = pte = pte_offset_kernel(pmd, addr);
> do {
> if (!pte_none(*pte)) {
> + pte_t old_pte = *pte;
> kvm_set_pte(pte, __pte(0));
> - put_page(virt_to_page(pte));
was this a bug beforehand that we released the page before we flushed
the TLB?
> kvm_tlb_flush_vmid_ipa(kvm, addr);
> + if ((pte_val(old_pte) & PAGE_S2_DEVICE) !=
> PAGE_S2_DEVICE)
> + kvm_flush_dcache_pte(old_pte);
this is confusing me: We are only flushing the cache for cached stage-2
mappings? Weren't we trying to flush the cache for uncached mappings?
(we obviously also need flush a cached stage-2 mapping but where the
guest is mapping it as uncached, but we don't know that easily).
Am I missing something completely here?
In any case we probably need a comment here explaining this.
> + put_page(virt_to_page(pte));
> }
> } while (pte++, addr += PAGE_SIZE, addr != end);
>
> @@ -149,8 +167,10 @@ static void unmap_pmds(struct kvm *kvm, pud_t *pud,
> next = kvm_pmd_addr_end(addr, end);
> if (!pmd_none(*pmd)) {
> if (kvm_pmd_huge(*pmd)) {
> + pmd_t old_pmd = *pmd;
> pmd_clear(pmd);
> kvm_tlb_flush_vmid_ipa(kvm, addr);
> + kvm_flush_dcache_pmd(old_pmd);
> put_page(virt_to_page(pmd));
> } else {
> unmap_ptes(kvm, pmd, addr, next);
> @@ -173,8 +193,10 @@ static void unmap_puds(struct kvm *kvm, pgd_t *pgd,
> next = kvm_pud_addr_end(addr, end);
> if (!pud_none(*pud)) {
> if (pud_huge(*pud)) {
> + pud_t old_pud = *pud;
> pud_clear(pud);
> kvm_tlb_flush_vmid_ipa(kvm, addr);
> + kvm_flush_dcache_pud(old_pud);
> put_page(virt_to_page(pud));
> } else {
> unmap_pmds(kvm, pud, addr, next);
> @@ -209,10 +231,8 @@ static void stage2_flush_ptes(struct kvm *kvm, pmd_t
> *pmd,
>
> pte = pte_offset_kernel(pmd, addr);
> do {
> - if (!pte_none(*pte)) {
> - hva_t hva = gfn_to_hva(kvm, addr >> PAGE_SHIFT);
> - kvm_flush_dcache_to_poc((void*)hva, PAGE_SIZE);
> - }
> + if (!pte_none(*pte))
> + kvm_flush_dcache_pte(*pte);
> } while (pte++, addr += PAGE_SIZE, addr != end);
> }
>
> @@ -226,12 +246,10 @@ static void stage2_flush_pmds(struct kvm *kvm, pud_t
> *pud,
> do {
> next = kvm_pmd_addr_end(addr, end);
> if (!pmd_none(*pmd)) {
> - if (kvm_pmd_huge(*pmd)) {
> - hva_t hva = gfn_to_hva(kvm, addr >> PAGE_SHIFT);
> - kvm_flush_dcache_to_poc((void*)hva, PMD_SIZE);
> - } else {
> + if (kvm_pmd_huge(*pmd))
> + kvm_flush_dcache_pmd(*pmd);
> + else
> stage2_flush_ptes(kvm, pmd, addr, next);
> - }
> }
> } while (pmd++, addr = next, addr != end);
> }
> @@ -246,12 +264,10 @@ static void stage2_flush_puds(struct kvm *kvm, pgd_t
> *pgd,
> do {
> next = kvm_pud_addr_end(addr, end);
> if (!pud_none(*pud)) {
> - if (pud_huge(*pud)) {
> - hva_t hva = gfn_to_hva(kvm, addr >> PAGE_SHIFT);
> - kvm_flush_dcache_to_poc((void*)hva, PUD_SIZE);
> - } else {
> + if (pud_huge(*pud))
> + kvm_flush_dcache_pud(*pud);
> + else
> stage2_flush_pmds(kvm, pud, addr, next);
> - }
> }
> } while (pud++, addr = next, addr != end);
> }
> diff --git a/arch/arm64/include/asm/kvm_mmu.h
> b/arch/arm64/include/asm/kvm_mmu.h
> index 14a74f1..b7419f5 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -260,6 +260,24 @@ static inline void coherent_cache_guest_page(struct
> kvm_vcpu *vcpu, hva_t hva,
>
> #define kvm_virt_to_phys(x) __virt_to_phys((unsigned long)(x))
>
> +static inline void __kvm_flush_dcache_pte(pte_t pte)
> +{
> + struct page *page = pte_page(pte);
> + kvm_flush_dcache_to_poc(page_address(page), PAGE_SIZE);
> +}
> +
> +static inline void __kvm_flush_dcache_pmd(pmd_t pmd)
> +{
> + struct page *page = pmd_page(pmd);
> + kvm_flush_dcache_to_poc(page_address(page), PMD_SIZE);
> +}
> +
> +static inline void __kvm_flush_dcache_pud(pud_t pud)
> +{
> + struct page *page = pud_page(pud);
> + kvm_flush_dcache_to_poc(page_address(page), PUD_SIZE);
> +}
> +
> void stage2_flush_vm(struct kvm *kvm);
>
> #endif /* __ASSEMBLY__ */
> --
> 2.1.4
>
Thanks,
-Christoffer
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