| Message ID | 20240320001542.3203871-4-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: Fix for a mostly benign gpc WARN | expand |
On Tue, 2024-03-19 at 17:15 -0700, Sean Christopherson wrote: > Explicit disallow activating a gfn_to_pfn_cache with an error gpa, i.e. > INVALID_GPA, to ensure that KVM doesn't mistake a GPA-based cache for an > HVA-based cache (KVM uses INVALID_GPA as a magic value to differentiate > between GPA-based and HVA-based caches). > > WARN if KVM attempts to activate a cache with INVALID_GPA, purely so that > new caches need to at least consider what to do with a "bad" GPA, as all > existing usage of kvm_gpc_activate() guarantees gpa != INVALID_GPA. I.e. > removing the WARN in the future is completely reasonable if doing so would > yield cleaner/better code overall. > > Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
On 20/03/2024 00:15, Sean Christopherson wrote: > Explicit disallow activating a gfn_to_pfn_cache with an error gpa, i.e. > INVALID_GPA, to ensure that KVM doesn't mistake a GPA-based cache for an > HVA-based cache (KVM uses INVALID_GPA as a magic value to differentiate > between GPA-based and HVA-based caches). > > WARN if KVM attempts to activate a cache with INVALID_GPA, purely so that > new caches need to at least consider what to do with a "bad" GPA, as all > existing usage of kvm_gpc_activate() guarantees gpa != INVALID_GPA. I.e. > removing the WARN in the future is completely reasonable if doing so would > yield cleaner/better code overall. > > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > virt/kvm/pfncache.c | 7 +++++++ > 1 file changed, 7 insertions(+) > Reviewed-by: Paul Durrant <paul@xen.org>
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c index 91b0e329006b..f618719644e0 100644 --- a/virt/kvm/pfncache.c +++ b/virt/kvm/pfncache.c @@ -418,6 +418,13 @@ static int __kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len) { + /* + * Explicitly disallow INVALID_GPA so that the magic value can be used + * by KVM to differentiate between GPA-based and HVA-based caches. + */ + if (WARN_ON_ONCE(kvm_is_error_gpa(gpa))) + return -EINVAL; + return __kvm_gpc_activate(gpc, gpa, KVM_HVA_ERR_BAD, len); }
Explicit disallow activating a gfn_to_pfn_cache with an error gpa, i.e. INVALID_GPA, to ensure that KVM doesn't mistake a GPA-based cache for an HVA-based cache (KVM uses INVALID_GPA as a magic value to differentiate between GPA-based and HVA-based caches). WARN if KVM attempts to activate a cache with INVALID_GPA, purely so that new caches need to at least consider what to do with a "bad" GPA, as all existing usage of kvm_gpc_activate() guarantees gpa != INVALID_GPA. I.e. removing the WARN in the future is completely reasonable if doing so would yield cleaner/better code overall. Signed-off-by: Sean Christopherson <seanjc@google.com> --- virt/kvm/pfncache.c | 7 +++++++ 1 file changed, 7 insertions(+)