[PATCH v9 17/41] KVM: SEV: Make 'uaddr' parameter optional for KVM_SEV_SNP_LAUNCH_UPDATE

[Ackerley Tng via B4 Relay]

From: Michael Roth <michael.roth@xxxxxxx>

Make the source page for populating an SNP guest_memfd instance optional
if in-place conversion/population is enabled.  If KVM can convert the page
in-place, then it's possible for guest memory to be initialized directly
from userspace by mmap()'ing the guest_memfd and writing to it while the
corresponding GPA ranges are in a 'shared' state, before converting them
to the 'private' state expected by KVM_SEV_SNP_LAUNCH_UPDATE.

Update the handling/documentation for KVM_SEV_SNP_LAUNCH_UPDATE to allow
for 'uaddr' to be set to NULL when in-place conversion is enabled, which
SNP_LAUNCH_UPDATE will then use to determine when it should/shouldn't
copy in data from a separate memory location. Continue to enforce
non-NULL when PRIVATE is tracked per-VM, not per-guest_memfd.

Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
[Moved condition to snp_launch_update]
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Tested-by: Shivank Garg <shivankg@xxxxxxx>
Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
 Documentation/virt/kvm/x86/amd-memory-encryption.rst | 14 ++++++++++----
 arch/x86/kvm/svm/sev.c                               | 11 ++++++-----
 virt/kvm/kvm_main.c                                  |  1 +
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
index bd04a908a8dbd..5977fbe33b98c 100644
--- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
+++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
@@ -503,7 +503,8 @@ secrets.
 
 It is required that the GPA ranges initialized by this command have had the
 KVM_MEMORY_ATTRIBUTE_PRIVATE attribute set in advance. See the documentation
-for KVM_SET_MEMORY_ATTRIBUTES for more details on this aspect.
+for KVM_SET_MEMORY_ATTRIBUTES/KVM_SET_MEMORY_ATTRIBUTES2 for more details on
+this aspect.
 
 Upon success, this command is not guaranteed to have processed the entire
 range requested. Instead, the ``gfn_start``, ``uaddr``, and ``len`` fields of
@@ -511,9 +512,14 @@ range requested. Instead, the ``gfn_start``, ``uaddr``, and ``len`` fields of
 remaining range that has yet to be processed. The caller should continue
 calling this command until those fields indicate the entire range has been
 processed, e.g. ``len`` is 0, ``gfn_start`` is equal to the last GFN in the
-range plus 1, and ``uaddr`` is the last byte of the userspace-provided source
-buffer address plus 1. In the case where ``type`` is KVM_SEV_SNP_PAGE_TYPE_ZERO,
-``uaddr`` will be ignored completely.
+range plus 1, and ``uaddr`` (if specified) is the last byte of the
+userspace-provided source buffer address plus 1.
+
+In the case where ``type`` is KVM_SEV_SNP_PAGE_TYPE_ZERO, ``uaddr`` will be
+ignored completely. For all other page types, ``uaddr`` is optional if in-place
+conversion is enabled (i.e. when the data had been written directly to
+guest_memfd while the page was in the shared state) and is required if in-place
+conversion is disabled.
 
 Parameters (in): struct  kvm_sev_snp_launch_update
 
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 90a08d36d843d..0f6fec21c1355 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2395,7 +2395,7 @@ static int sev_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
 	 */
 	if (ret && !snp_page_reclaim(kvm, pfn) &&
 	    sev_populate_args->type == KVM_SEV_SNP_PAGE_TYPE_CPUID &&
-	    sev_populate_args->fw_error == SEV_RET_INVALID_PARAM) {
+	    sev_populate_args->fw_error == SEV_RET_INVALID_PARAM && src_page) {
 		void *src_vaddr = kmap_local_page(src_page);
 		void *dst_vaddr = kmap_local_pfn(pfn);
 
@@ -2428,8 +2428,8 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	if (copy_from_user(&params, u64_to_user_ptr(argp->data), sizeof(params)))
 		return -EFAULT;
 
-	pr_debug("%s: GFN start 0x%llx length 0x%llx type %d flags %d\n", __func__,
-		 params.gfn_start, params.len, params.type, params.flags);
+	pr_debug("%s: GFN start 0x%llx length 0x%llx type %d flags %d src %llx\n", __func__,
+		 params.gfn_start, params.len, params.type, params.flags, params.uaddr);
 
 	if (!params.len || !PAGE_ALIGNED(params.len) || params.flags ||
 	    (params.type != KVM_SEV_SNP_PAGE_TYPE_NORMAL &&
@@ -2441,7 +2441,8 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp)
 
 	if (params.type == KVM_SEV_SNP_PAGE_TYPE_ZERO)
 		src = NULL;
-	else if (!params.uaddr || !PAGE_ALIGNED(params.uaddr))
+	else if ((!gmem_in_place_conversion && !params.uaddr) ||
+		 !PAGE_ALIGNED(params.uaddr))
 		return -EINVAL;
 	else
 		src = u64_to_user_ptr(params.uaddr);
@@ -2488,7 +2489,7 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp)
 
 	params.gfn_start += count;
 	params.len -= count * PAGE_SIZE;
-	if (params.type != KVM_SEV_SNP_PAGE_TYPE_ZERO)
+	if (src && params.type != KVM_SEV_SNP_PAGE_TYPE_ZERO)
 		params.uaddr += count * PAGE_SIZE;
 
 	if (copy_to_user(u64_to_user_ptr(argp->data), &params, sizeof(params)))
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f0f802eaca16b..e961cc297ba2a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -103,6 +103,7 @@ module_param(allow_unsafe_mappings, bool, 0444);
 
 #ifdef kvm_arch_has_private_mem
 bool __ro_after_init gmem_in_place_conversion = false;
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(gmem_in_place_conversion);
 #endif
 
 /*

-- 
2.55.0.508.g3f0d502094-goog