From: David Matlack <dmatlack@google.com>
To: Vishal Annapurve <vannapurve@google.com>
Cc: x86@kernel.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
pbonzini@redhat.com, shuah@kernel.org, bgardon@google.com,
seanjc@google.com, oupton@google.com, peterx@redhat.com,
vkuznets@redhat.com, drjones@redhat.com
Subject: Re: [V1 PATCH 3/5] selftests: kvm: x86: Execute vmcall/vmmcall according to CPU type
Date: Thu, 8 Sep 2022 15:54:41 -0700 [thread overview]
Message-ID: <YxpysbHZb2G56K+f@google.com> (raw)
In-Reply-To: <20220903012849.938069-4-vannapurve@google.com>
Please use "KVM: selftest: ..." for the shortlog.
On Sat, Sep 03, 2022 at 01:28:47AM +0000, Vishal Annapurve wrote:
> Modify following APIs for x86 implementation:
> 1) kvm_arch_main : Query the cpu vendor and cache the value in advance.
> 2) kvm_arch_post_vm_load: Populate cpu type in the guest memory so that
> guest doesn't need to execute cpuid instruction again.
This commit message only describes a subset of the changes in this
commit, and does not provide any context on why the changes are being
made (other than a clue about avoiding CPUID).
I also think this could be split up into 2 separate commits.
I would suggest first patch changes is_{intel,amd}_cpu() to return a cached
result. e.g.
KVM: selftests: Precompute the result for is_{intel,amd}_cpu()
Cache the vendor CPU type in a global variable so that multiple calls
to is_intel_cpu() do not need to re-execute CPUID. This will be useful
in a follow-up commit to check if running on AMD or Intel from within
a selftest guest where executing CPUID requires a VM-exit.
Then add support for AMD to kvm_hypercall():
KVM: selftests: Add AMD support to kvm_hypercall()
Add support for AMD hypercalls to kvm_hypercall() so that it can be
used in selftests running on Intel or AMD hosts. This will be used in
a follow up commit to ...
As part of this change, sync the global variable is_cpu_amd into the
guest so the guest can determine which hypercall instruction to use
without needing to re-execute CPUID for every hypercall.
>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Vishal Annapurve <vannapurve@google.com>
> ---
> .../testing/selftests/kvm/lib/x86_64/processor.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> index e22cfc4bf284..ac104653ab43 100644
> --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
> +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> @@ -19,6 +19,7 @@
> #define MAX_NR_CPUID_ENTRIES 100
>
> vm_vaddr_t exception_handlers;
> +static int is_cpu_amd = -1;
Should this just be a bool? Since you are initializing it before main(),
there is really no way for any code to observe it's pre-initialized
value. And nothing even checks if is_cpu_amd -1, it just silently
returns false from is_intel_cpu() and is_amd_cpu().
>
> static void regs_dump(FILE *stream, struct kvm_regs *regs, uint8_t indent)
> {
> @@ -1019,7 +1020,7 @@ static bool cpu_vendor_string_is(const char *vendor)
>
> bool is_intel_cpu(void)
> {
> - return cpu_vendor_string_is("GenuineIntel");
> + return (is_cpu_amd == 0);
> }
>
> /*
> @@ -1027,7 +1028,7 @@ bool is_intel_cpu(void)
> */
> bool is_amd_cpu(void)
> {
> - return cpu_vendor_string_is("AuthenticAMD");
> + return (is_cpu_amd == 1);
> }
>
> void kvm_get_cpu_address_width(unsigned int *pa_bits, unsigned int *va_bits)
> @@ -1182,9 +1183,15 @@ uint64_t kvm_hypercall(uint64_t nr, uint64_t a0, uint64_t a1, uint64_t a2,
> {
> uint64_t r;
>
> - asm volatile("vmcall"
> + if (is_amd_cpu())
> + asm volatile("vmmcall"
> : "=a"(r)
> : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3));
> + else
> + asm volatile("vmcall"
> + : "=a"(r)
> + : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3));
> +
> return r;
> }
>
> @@ -1314,8 +1321,10 @@ bool vm_is_unrestricted_guest(struct kvm_vm *vm)
>
> void kvm_arch_main(void)
> {
> + is_cpu_amd = cpu_vendor_string_is("AuthenticAMD") ? 1 : 0;
> }
>
> void kvm_arch_post_vm_load(struct kvm_vm *vm)
> {
> + sync_global_to_guest(vm, is_cpu_amd);
> }
> --
> 2.37.2.789.g6183377224-goog
>
next prev parent reply other threads:[~2022-09-08 22:55 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-03 1:28 [V1 PATCH 0/5] Execute hypercalls from guests according to cpu type Vishal Annapurve
2022-09-03 1:28 ` [V1 PATCH 1/5] selftests: kvm: move common startup logic to kvm_util.c Vishal Annapurve
2022-09-08 21:09 ` David Matlack
2022-09-14 19:09 ` Vishal Annapurve
2022-09-03 1:28 ` [V1 PATCH 2/5] selftests: kvm: Introduce kvm_arch_main and helpers Vishal Annapurve
2022-09-05 7:46 ` Andrew Jones
2022-09-06 22:46 ` Vishal Annapurve
2022-09-08 21:21 ` David Matlack
2022-09-09 7:01 ` Andrew Jones
2022-09-14 19:13 ` Vishal Annapurve
2022-09-08 21:27 ` David Matlack
2022-09-03 1:28 ` [V1 PATCH 3/5] selftests: kvm: x86: Execute vmcall/vmmcall according to CPU type Vishal Annapurve
2022-09-08 22:54 ` David Matlack [this message]
2022-09-08 22:57 ` David Matlack
2022-09-14 19:12 ` Vishal Annapurve
2022-09-03 1:28 ` [V1 PATCH 4/5] selftests: kvm: delete svm_vmcall_test Vishal Annapurve
2022-09-03 1:28 ` [V1 PATCH 5/5] selftests: kvm: Execute vmcall/vmmcall as per cpu type Vishal Annapurve
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YxpysbHZb2G56K+f@google.com \
--to=dmatlack@google.com \
--cc=bgardon@google.com \
--cc=drjones@redhat.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=oupton@google.com \
--cc=pbonzini@redhat.com \
--cc=peterx@redhat.com \
--cc=seanjc@google.com \
--cc=shuah@kernel.org \
--cc=vannapurve@google.com \
--cc=vkuznets@redhat.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).