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KVM: SEV: Make 'uaddr' parameter optional for KVM_SEV_SNP_LAUNCH_UPDATE

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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.

[ Sean: Moved condition to snp_launch_update ]

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Tested-by: Shivank Garg <shivankg@amd.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Link: https://patch.msgid.link/20260910-gmem-inplace-conversion-v13-19-dd6fbf94f4e1@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Michael Roth 2026-09-10 16:55:45 -07:00 committed by Sean Christopherson
parent cb0544296a
commit edcc3f4298
3 changed files with 17 additions and 9 deletions
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14
Documentation/virt/kvm/x86/amd-memory-encryption.rst
View File

@ -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

11
arch/x86/kvm/svm/sev.c
View File

@ -2400,7 +2400,7 @@ 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);
@ -2433,8 +2433,8 @@ 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 &&
@ -2446,7 +2446,8 @@ 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);
@ -2493,7 +2494,7 @@ 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)))

1
virt/kvm/kvm_main.c
View File

@ -104,6 +104,7 @@ 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
/*