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Re: [RFC PATCH] xen: Introduce arch specific field to XEN_SYSCTL_physinfo

On 30.08.21 16:16, Jan Beulich wrote:

Hi Jan

On 29.08.2021 22:28, Oleksandr wrote:
On 16.08.21 10:33, Jan Beulich wrote:
On 14.08.2021 01:28, Oleksandr Tyshchenko wrote:
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -332,6 +332,11 @@ struct xen_arch_domainconfig {
       uint32_t clock_frequency;
+struct arch_physinfo {
+    /* Holds the bit size of IPAs in p2m tables. */
+    uint32_t p2m_ipa_bits;
   #endif /* __XEN__ || __XEN_TOOLS__ */
struct arch_vcpu_info {
--- a/xen/include/public/arch-x86/xen.h
+++ b/xen/include/public/arch-x86/xen.h
@@ -346,6 +346,8 @@ typedef struct xen_msr_entry {
   } xen_msr_entry_t;
+struct arch_physinfo {
   #endif /* !__ASSEMBLY__ */
While the term "p2m_ipa_bits" surely isn't arch-agnostic, I wonder
whether the expressed information is (the x86 equivalent being
hap_paddr_bits, at a guess), and hence whether this really ought
to live in an arch-specific sub-struct.
Well, on Arm we calculate the number of the IPA bits based on the number
of PA bits when setting Stage 2 address translation.
I might mistake, but what we currently have on Arm is "ipa_bits ==
pa_bits". So, this means that information we need at the toolstack side
isn't really arch-specific and
we could probably avoid introducing arch-specific sub-struct by suitable
renaming the field (pa_bits, paddr_bits, whatever).

We could even name the field as hap_paddr_bits. Although, I don't know
whether the hap_* is purely x86-ism, but I see there are several
mentions in the common code (hap_pt_share, use_hap_pt, etc). Any
Well, HAP or not - there is going to be a limit to a guest's
address bits. So I don't see why it would matter whether HAP is
an x86-specific term.


  If you wanted to express the guest nature
and distinguish it from "paddr_bits", how about "gaddr_bits" or

ok, both sound fine to me, with a little preference for gpaddr_bits. So, will drop arch-specific sub-struct for the next version.

Thank you.



Oleksandr Tyshchenko



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