Re: [RFC PATCH v1 2/4] kvmppc: Add support for shared pages in HMM driver
From: Paul Mackerras <hidden>
Date: 2018-10-30 05:31:15
Also in:
linux-mm
On Mon, Oct 22, 2018 at 10:48:35AM +0530, Bharata B Rao wrote:
A secure guest will share some of its pages with hypervisor (Eg. virtio bounce buffers etc). Support shared pages in HMM driver. Signed-off-by: Bharata B Rao <redacted>
Comments below...
quoted hunk ↗ jump to hunk
--- arch/powerpc/kvm/book3s_hv_hmm.c | 69 ++++++++++++++++++++++++++++++-- 1 file changed, 65 insertions(+), 4 deletions(-)diff --git a/arch/powerpc/kvm/book3s_hv_hmm.c b/arch/powerpc/kvm/book3s_hv_hmm.c index a2ee3163a312..09b8e19b7605 100644 --- a/arch/powerpc/kvm/book3s_hv_hmm.c +++ b/arch/powerpc/kvm/book3s_hv_hmm.c@@ -50,6 +50,7 @@ struct kvmppc_hmm_page_pvt { struct hlist_head *hmm_hash; unsigned int lpid; unsigned long gpa; + bool skip_page_out; }; struct kvmppc_hmm_migrate_args {@@ -278,6 +279,65 @@ static unsigned long kvmppc_gpa_to_hva(struct kvm *kvm, unsigned long gpa, return hva; } +/* + * Shares the page with HV, thus making it a normal page. + * + * - If the page is already secure, then provision a new page and share + * - If the page is a normal page, share the existing page + * + * In the former case, uses the HMM fault handler to release the HMM page. + */ +static unsigned long +kvmppc_share_page(struct kvm *kvm, unsigned long gpa, + unsigned long addr, unsigned long page_shift) +{ + + int ret; + struct hlist_head *list, *hmm_hash; + unsigned int lpid = kvm->arch.lpid; + unsigned long flags; + struct kvmppc_hmm_pfn_entry *p; + struct page *hmm_page, *page; + struct kvmppc_hmm_page_pvt *pvt; + unsigned long pfn; + + /* + * First check if the requested page has already been given to + * UV as a secure page. If so, ensure that we don't issue a + * UV_PAGE_OUT but instead directly send the page + */ + spin_lock_irqsave(&kvmppc_hmm_lock, flags); + hmm_hash = kvm->arch.hmm_hash; + list = &hmm_hash[kvmppc_hmm_pfn_hash_fn(gpa)]; + hlist_for_each_entry(p, list, hlist) { + if (p->addr == gpa) { + hmm_page = pfn_to_page(p->hmm_pfn); + get_page(hmm_page); /* TODO: Necessary ? */ + pvt = (struct kvmppc_hmm_page_pvt *) + hmm_devmem_page_get_drvdata(hmm_page); + pvt->skip_page_out = true; + put_page(hmm_page); + break; + } + } + spin_unlock_irqrestore(&kvmppc_hmm_lock, flags); + + ret = get_user_pages_fast(addr, 1, 0, &page);
Why are we calling this with write==0? Surely in general the secure guest will expect to be able to write to the shared page? Also, in general get_user_pages_fast isn't sufficient to translate a host virtual address (derived from a guest real address) into a pfn. See for example hva_to_pfn() in virt/kvm/kvm_main.c and the things it does to cope with the various cases that one can hit. I can imagine in future that the secure guest might want to establish a shared mapping to a PCI device, for instance.
+ if (ret != 1)
+ return H_PARAMETER;
+
+ pfn = page_to_pfn(page);
+ if (is_zero_pfn(pfn)) {
+ put_page(page);
+ return H_SUCCESS;
+ }The ultravisor still needs a page to map into the guest in this case, doesn't it? What's the point of returning without giving the ultravisor a page to use?
quoted hunk ↗ jump to hunk
+ + ret = uv_page_in(lpid, pfn << page_shift, gpa, 0, page_shift); + put_page(page); + + return (ret == U_SUCCESS) ? H_SUCCESS : H_PARAMETER; +} + /* * Move page from normal memory to secure memory. */@@ -300,8 +360,8 @@ kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa, return H_PARAMETER; end = addr + (1UL << page_shift); - if (flags) - return H_P2; + if (flags & H_PAGE_IN_SHARED) + return kvmppc_share_page(kvm, gpa, addr, page_shift);
Would be best to fail if any unknown flags are set, I would think.
quoted hunk ↗ jump to hunk
args.hmm_hash = kvm->arch.hmm_hash; args.lpid = kvm->arch.lpid;@@ -349,8 +409,9 @@ kvmppc_hmm_fault_migrate_alloc_and_copy(struct vm_area_struct *vma, hmm_devmem_page_get_drvdata(spage); pfn = page_to_pfn(dpage); - ret = uv_page_out(pvt->lpid, pfn << PAGE_SHIFT, - pvt->gpa, 0, PAGE_SHIFT); + if (!pvt->skip_page_out) + ret = uv_page_out(pvt->lpid, pfn << PAGE_SHIFT, + pvt->gpa, 0, PAGE_SHIFT); if (ret == U_SUCCESS) *dst_pfn = migrate_pfn(pfn) | MIGRATE_PFN_LOCKED; }-- 2.17.1
Paul.