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Message-ID: <ZYJUIsQM06mhzOTY@yilunxu-OptiPlex-7050>
Date: Wed, 20 Dec 2023 10:40:34 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Paul Durrant <paul@....org>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>,
Sean Christopherson <seanjc@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
David Woodhouse <dwmw2@...radead.org>,
Shuah Khan <shuah@...nel.org>, kvm@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v11 08/19] KVM: pfncache: allow a cache to be activated
with a fixed (userspace) HVA
On Tue, Dec 19, 2023 at 04:10:58PM +0000, Paul Durrant wrote:
> From: Paul Durrant <pdurrant@...zon.com>
>
> Some pfncache pages may actually be overlays on guest memory that have a
> fixed HVA within the VMM. It's pointless to invalidate such cached
> mappings if the overlay is moved so allow a cache to be activated directly
> with the HVA to cater for such cases. A subsequent patch will make use
> of this facility.
>
> Signed-off-by: Paul Durrant <pdurrant@...zon.com>
> Reviewed-by: David Woodhouse <dwmw@...zon.co.uk>
> ---
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: David Woodhouse <dwmw2@...radead.org>
>
> v11:
> - Fixed kvm_gpc_check() to ignore memslot generation if the cache is not
> activated with a GPA. (This breakage occured during the re-work for v8).
>
> v9:
> - Pass both GPA and HVA into __kvm_gpc_refresh() rather than overloading
> the address paraneter and using a bool flag to indicated what it is.
>
> v8:
> - Re-worked to avoid messing with struct gfn_to_pfn_cache.
> ---
> include/linux/kvm_host.h | 20 +++++++++++++++++++-
> virt/kvm/pfncache.c | 40 +++++++++++++++++++++++++++++++---------
> 2 files changed, 50 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6097f076a7b0..8120674b87b0 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1345,6 +1345,22 @@ void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm);
> */
> int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len);
>
> +/**
> + * kvm_gpc_activate_hva - prepare a cached kernel mapping and HPA for a given HVA.
> + *
> + * @gpc: struct gfn_to_pfn_cache object.
> + * @hva: userspace virtual address to map.
> + * @len: sanity check; the range being access must fit a single page.
> + *
> + * @return: 0 for success.
> + * -EINVAL for a mapping which would cross a page boundary.
> + * -EFAULT for an untranslatable guest physical address.
> + *
> + * The semantics of this function are the same as those of kvm_gpc_activate(). It
> + * merely bypasses a layer of address translation.
> + */
> +int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long hva, unsigned long len);
> +
> /**
> * kvm_gpc_check - check validity of a gfn_to_pfn_cache.
> *
> @@ -1399,7 +1415,9 @@ void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc);
> static inline void kvm_gpc_mark_dirty(struct gfn_to_pfn_cache *gpc)
> {
> lockdep_assert_held(&gpc->lock);
> - mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
> +
> + if (gpc->gpa != KVM_XEN_INVALID_GPA)
> + mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
> }
>
> void kvm_sigset_activate(struct kvm_vcpu *vcpu);
> diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
> index 97eec8ee3449..ae822bff812f 100644
> --- a/virt/kvm/pfncache.c
> +++ b/virt/kvm/pfncache.c
> @@ -48,7 +48,10 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
> if (!gpc->active)
> return false;
>
> - if (gpc->generation != slots->generation || kvm_is_error_hva(gpc->uhva))
> + if (gpc->gpa != KVM_XEN_INVALID_GPA && gpc->generation != slots->generation)
> + return false;
> +
> + if (kvm_is_error_hva(gpc->uhva))
> return false;
>
> if (offset_in_page(gpc->uhva) + len > PAGE_SIZE)
> @@ -209,11 +212,13 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
> return -EFAULT;
> }
>
> -static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
> +static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
> unsigned long len)
> {
> struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
> - unsigned long page_offset = offset_in_page(gpa);
> + unsigned long page_offset = (gpa != KVM_XEN_INVALID_GPA) ?
> + offset_in_page(gpa) :
> + offset_in_page(uhva);
> bool unmap_old = false;
> unsigned long old_uhva;
> kvm_pfn_t old_pfn;
> @@ -246,9 +251,15 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
> old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
> old_uhva = PAGE_ALIGN_DOWN(gpc->uhva);
>
> - /* Refresh the userspace HVA if necessary */
> - if (gpc->gpa != gpa || gpc->generation != slots->generation ||
> - kvm_is_error_hva(gpc->uhva)) {
> + if (gpa == KVM_XEN_INVALID_GPA) {
> + gpc->gpa = KVM_XEN_INVALID_GPA;
> + gpc->uhva = PAGE_ALIGN_DOWN(uhva);
> +
> + if (gpc->uhva != old_uhva)
> + hva_change = true;
> + } else if (gpc->gpa != gpa ||
> + gpc->generation != slots->generation ||
> + kvm_is_error_hva(gpc->uhva)) {
> gfn_t gfn = gpa_to_gfn(gpa);
>
> gpc->gpa = gpa;
> @@ -319,7 +330,7 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
>
> int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
> {
> - return __kvm_gpc_refresh(gpc, gpc->gpa, len);
> + return __kvm_gpc_refresh(gpc, gpc->gpa, gpc->uhva, len);
> }
>
> void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
> @@ -332,7 +343,8 @@ void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
> gpc->uhva = KVM_HVA_ERR_BAD;
> }
>
> -int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
> +static int __kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
> + unsigned long len)
> {
> struct kvm *kvm = gpc->kvm;
>
> @@ -353,7 +365,17 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
> gpc->active = true;
> write_unlock_irq(&gpc->lock);
> }
> - return __kvm_gpc_refresh(gpc, gpa, len);
> + return __kvm_gpc_refresh(gpc, gpa, uhva, len);
> +}
> +
> +int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
> +{
> + return __kvm_gpc_activate(gpc, gpa, KVM_HVA_ERR_BAD, len);
> +}
> +
> +int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long uhva, unsigned long len)
> +{
> + return __kvm_gpc_activate(gpc, KVM_XEN_INVALID_GPA, uhva, len);
> }
>
> void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
The code looks good to me, but I feel odd that a *gfn*_to_pfn_cache is
used, but gfn is not taken into account.
I think if it is possible we introduce an hva_to_pfn_cache(hpc) that
actually does most of the job in this file. Xen could directly use hpc,
and gfn_to_pfn_cache works on top of hpc.
BTW: I also see there is a gfn_to_hva_cache which does pretty much the
same as gpc's first half job. Is it possible to unify them like:
struct gfn_to_pfn_cache {
struct gfn_to_hva_cache ghc;
struct hva_to_pfn_cache hpc;
...
}
Just my two cents.
Thanks,
Yilun
> --
> 2.39.2
>
>
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